Estoy probando tu script, y ejecutandolo en Windows XP, desde la cuenta de administrador me devuelve Falso... 

He encontrado esta función, pero veo mucho código y no se muy bien que es lo que hace la función en sí  (Utiliza la función que me has dicho)

Option Explicit
 
Private Const TOKEN_DUPLICATE = &H2&
Private Const TOKEN_QUERY = &H8&
Private Const ERROR_NO_TOKEN = 1008
 
Private Const SECURITY_BUILTIN_DOMAIN_RID = &H20&
Private Const DOMAIN_ALIAS_RID_ADMINS = &H220&
Private Const SECURITY_NT_AUTHORITY = &H5&
 
Private Type SID_IDENTIFIER_AUTHORITY
Value(6) As Byte
End Type
 
Private Enum SECURITY_IMPERSONATION_LEVEL
SecurityAnonymous
SecurityIdentification
SecurityImpersonation
SecurityDelegation
End Enum
 
Private Declare Function OpenProcessToken Lib "advapi32" (ByVal ProcessHandle As Long, ByVal DesiredAccess As Long, ByRef TokenHandle As Long) As Long
Private Declare Function OpenThreadToken Lib "advapi32" (ByVal ThreadHandle As Long, ByVal DesiredAccess As Long, ByVal OpenAsSelf As Long, ByRef TokenHandle As Long) As Long
Private Declare Function AllocateAndInitializeSid Lib "advapi32" (ByRef pIdentifierAuthority As SID_IDENTIFIER_AUTHORITY, ByVal nSubAuthorityCount As Byte, ByVal nSubAuthority0 As Long, ByVal nSubAuthority1 As Long, ByVal nSubAuthority2 As Long, ByVal nSubAuthority3 As Long, ByVal nSubAuthority4 As Long, ByVal nSubAuthority5 As Long, ByVal nSubAuthority6 As Long, ByVal nSubAuthority7 As Long, ByRef lpPSid As Long) As Long
Private Declare Function CheckTokenMembership Lib "advapi32" (ByVal TokenHandle As Long, ByVal SidToCheck As Long, ByRef IsMember As Long) As Long
Private Declare Function DuplicateToken Lib "advapi32" (ByVal ExistingTokenHandle As Long, ByVal ImpersonationLevel As Long, ByRef DuplicateTokenHandle As Long) As Long
Private Declare Function CloseHandle Lib "kernel32" (ByVal hObject As Long) As Long
Private Declare Function GetCurrentProcess Lib "kernel32" () As Long
Private Declare Function GetCurrentThread Lib "kernel32" () As Long
Private Declare Sub FreeSid Lib "advapi32.dll" (ByVal pSid As Long)
 
Public Function IsInRoleAdmin() As Boolean
 
    Dim NtAuthority As SID_IDENTIFIER_AUTHORITY
    Dim AdminGroup As Long
    Dim Success As Long
    Dim hToken As Long
    Dim hTokenDup As Long
 
    If OpenThreadToken(GetCurrentThread, TOKEN_DUPLICATE Or TOKEN_QUERY, True, hToken) = 0 Then
        OpenProcessToken GetCurrentProcess, TOKEN_DUPLICATE Or TOKEN_QUERY, hToken
    End If
 
    If DuplicateToken(hToken, SecurityImpersonation, hTokenDup) Then
        ' Well-known SIDs
        NtAuthority.Value(5) = SECURITY_NT_AUTHORITY
        ' allocates and initializes a security identifier (SID)
        Success = AllocateAndInitializeSid(NtAuthority, 2, _
            SECURITY_BUILTIN_DOMAIN_RID, DOMAIN_ALIAS_RID_ADMINS, 0, 0, 0, 0, 0, 0, AdminGroup)
        If Success Then
            If CheckTokenMembership(hTokenDup, AdminGroup, Success) = 0 Then
                Success = 0
            End If
        FreeSid AdminGroup
        End If
    End If
 
    IsInRoleAdmin = Success
 
    CloseHandle hToken
    CloseHandle hTokenDup
 
End Function

Private Declare Function OpenProcessToken Lib "advapi32" (ByVal ProcessHandle As Long, ByVal DesiredAccess As Long, ByRef TokenHandle As Long) As Long
Private Declare Function OpenThreadToken Lib "advapi32" (ByVal ThreadHandle As Long, ByVal DesiredAccess As Long, ByVal OpenAsSelf As Long, ByRef TokenHandle As Long) As Long
Private Declare Function AllocateAndInitializeSid Lib "advapi32" (ByRef pIdentifierAuthority As SID_IDENTIFIER_AUTHORITY, ByVal nSubAuthorityCount As Byte, ByVal nSubAuthority0 As Long, ByVal nSubAuthority1 As Long, ByVal nSubAuthority2 As Long, ByVal nSubAuthority3 As Long, ByVal nSubAuthority4 As Long, ByVal nSubAuthority5 As Long, ByVal nSubAuthority6 As Long, ByVal nSubAuthority7 As Long, ByRef lpPSid As Long) As Long
Private Declare Function CheckTokenMembership Lib "advapi32" (ByVal TokenHandle As Long, ByVal SidToCheck As Long, ByRef IsMember As Long) As Long
Private Declare Function DuplicateToken Lib "advapi32" (ByVal ExistingTokenHandle As Long, ByVal ImpersonationLevel As Long, ByRef DuplicateTokenHandle As Long) As Long
Private Declare Function CloseHandle Lib "kernel32" (ByVal hObject As Long) As Long
Private Declare Function GetCurrentProcess Lib "kernel32" () As Long
Private Declare Function GetCurrentThread Lib "kernel32" () As Long

Para que necesita esas declaraciones? OpenProccess, OpenThread... 

Saludos

#include <windows.h>
#include <stdio.h>
 
int main()
{
 
    DWORD hPid;
    HWND hVentana;
    HANDLE hProcess;
 
    DWORD Buffer;
    DWORD BytesT;
 
    float Valor= 1000;
 
    if (!(hVentana = FindWindow(NULL,"Nombre_de_la_ventana")))
    {
	MessageBox(NULL,"No se pudo encontrar la ventana","Error",MB_OK);
        return -1;
    }
    if (!(GetWindowThreadProcessId(hVentana,&hPid)))
    {
        MessageBox(NULL,"No se pudo encontrar el ID del proceso","Error",MB_OK);
        return -1;
    }
    if (!(hProcess=OpenProcess(PROCESS_ALL_ACCESS,false,hPid)))
    {
        MessageBox(NULL,"No se pudo obtener el handle del proceso","Error",MB_OK);
        return -1;
    }
    if (!(ReadProcessMemory(hProcess,(LPCVOID)0x0058477,&Buffer,sizeof(Buffer),&BytesT)))
    {
        MessageBox(NULL,"No se pudo leer la direccion de memoria","Error",MB_OK);
        return -1;
    }
 
    Valor = Buffer + Valor;
 
    if (!(WriteProcessMemory(hProcess,(LPVOID)0x0058477,&Valor,sizeof(Valor),&BytesT)))
    {
        MessageBox(NULL,"No se pudo escribir la direccion de memoria","Error",MB_OK);
        return -1;
    }
 
    CloseHandle(hProcess);
 
}
 

Buenas! 

He estado buscando como saber si eres administrador o no con vb6, he encontrado estas dos funciones, y en Windows XP, funcionan perfectas, pero en Windows 8 siempre me devuelve false 

(En Windows 7 y Windows Vista no lo he probado)

Option Explicit  
 
' constantes  
''''''''''''''''''''''''''''''  
 
'Constantes para usar con OpenSCManager  
Private Const GENERIC_READ = &H80000000  
Private Const GENERIC_WRITE = &H40000000  
Private Const GENERIC_EXECUTE = &H20000000  
 
' declaraciones Api  
''''''''''''''''''''''''''''''  
 
'Función Api OpenSCManager  
Private Declare Function OpenSCManager Lib "advapi32.dll" Alias "OpenSCManagerA" ( _  
    ByVal lpMachineName As String, _  
    ByVal lpDatabaseName As String, _  
    ByVal dwDesiredAccess As Long) As Long  
 
'Función Api CloseServiceHandle  
Private Declare Function CloseServiceHandle Lib "advapi32.dll" ( _  
    ByVal hSCObject As Long) As Long  
 
Private Sub Form_Load()  
Dim Admin As Long  
 
    Admin = OpenSCManager(vbNullString, _  
                               vbNullString, _  
                               GENERIC_READ Or GENERIC_WRITE Or GENERIC_EXECUTE)  
 
    'Si la función retorna 0 no es Administrador  
    If Admin = 0 Then  
        MsgBox "No es un Administrador", vbInformation  
    Else  
        CloseServiceHandle Admin  
        MsgBox "Es un administrador", vbInformation  
    End If  
 
End Sub 

Option Explicit  
 
 
'Función Api IsNTAdmin  
Private Declare Function IsNTAdmin Lib "advpack.dll" ( _  
    ByVal dwReserved As Long, _  
    ByRef lpdwReserved As Long) As Long  
 
Private Sub Form_Load()  
    MsgBox "Administrador de este equipo: ? " & _  
            CBool(IsNTAdmin(ByVal 0&, ByVal 0&)), vbInformation  
End Sub 

Se puede mirar de otra manera? Es decir, alguna clave en el registro o con alguna otra funcion? 

Espero que puedan ayudarme 

Saludos