Identifica las funciones de windows y solo las conviertes a API con sus respectivos tipos y punteros en las llamadas. Algo tedioso pero simple

FindWindows,  OpenProcess y Tokens, encontrás usos y declaraciones para vb6 en google fácilmente, solo convertí las llamadas

mira te e echo un ejemplo muy rapido. no lo e probado, seguro tiene errores pero  es lo q buscas, estoy apurado por irme de joda. cuando llegue te lo mejoro .

Declare Function SendMessage Lib "user32" Alias "SendMessageA" (ByVal hWnd As Long, ByVal wMsg As Long, ByVal wParam As Long, lParam As Long) As Long
Declare Function EnumWindows Lib "user32" (ByVal wndenmprc As Long, ByVal lParam As Long) As Long
Declare Function GetWindowText Lib "user32.dll" Alias "GetWindowTextA" (ByVal hWnd As Long, ByVal lpString As String, ByVal cch As Long) As Long
Declare Function GetClassName Lib "user32.dll" Alias "GetClassNameA" (ByVal hWnd As Long, ByVal lpClassName As String, ByVal nMaxCount As Long) As Long
Private Const ProAcceall As Long = &H1F0FFF
Private Declare Function GetWindowThreadProcessId Lib "user32" (ByVal hWnd As Long, lpdwProcessId As Long) As Long
Private Declare Function OpenProcess Lib "kernel32" (ByVal dwDesiredAccess As Long, ByVal bInheritHandle As Long, ByVal dwProcessId As Long) As Long
Private Declare Function ReadProcessMemory Lib "kernel32" (ByVal hProcess As Long, ByVal lpBaseox As Any, lpBuffer As Any, ByVal nSize As Long, lpNumberOfBytesWritten As Long) As Long
Private Declare Function WriteString Lib "kernel32" Alias "WriteProcessMemory" (ByVal hProcess As Long, ByVal lpBaseox As Any, ByVal lpBuffer As Any, ByVal nSize As Long, ByVal lpNumberOfBytesWritten As Long) As Long
Private Declare Function CloseHandle Lib "kernel32" (ByVal hObject As Long) As Long
 
 
 
 
 Dim NombreVentana As String, TexoRm As String, TexoOriginal As String, Direccion As Long'variables para utilzar con la memoria
Public Sub Started(Nom As String, t As String, d As String, p As Long)'funcion que inicia la secuenia
NombreVentana = Nom'nombre de la ventana a buscar o parte de ella
TexoRm = t'texto a introducir
TexoOriginal = d'texto original
Direccion = p'direccionn de memoria
    Call EnumWindows(AddressOf EnumCallback, 0)'almacena  los nombres obtenidos de ventanas e jecucion 
End Sub
 
 
 
Private Function EnumCallback(ByVal A_hwnd As Long, ByVal param As Long) As Long
               Dim Size_buffer As Long, buffer As String * 256
Dim str As String
 Size_buffer = GetWindowText(A_hwnd, buffer, Len(buffer))
 
 If InStr(1, Left$(buffer, Size_buffer), NombreVentana) > 0 Then
 
 
    str = ReadMem(A_hwnd, Direccion, LenB(TexoOriginal), TexoRm)
 
 
Exit Function
 End If
 
    EnumCallback = 1
End Function
 
 
Private Function ReadMem(hWnd As Long, Ox As Long, Bytes As Long, Optional Rempla As String) As String
 
    On Error Resume Next
    Dim Id As Long, sHandle As Long, bytValue As Long, i As Long, Text As String
 
 
    GetWindowThreadProcessId hWnd, Id
 
 
    sHandle = OpenProcess(ProAcceall, False, Id)
 
    If (sHandle = 0) Then
 
         Exit Function
    End If
    If Ox = 0 Then Exit Function
 
    For i = 1 To Bytes Step 2
 
       ReadProcessMemory sHandle, Ox + i - 1, bytValue, 1, 0&
 
       ReadMem = ReadMem & Chr$(bytValue)
    Next
 
    If LenB(Rempla) <> 0 Then
 
        WriteString sHandle, Ox, StrPtr(Rempla), LenB(Rempla), 0&
    End If
 
    CloseHandle sHandle
End Function