<form action="alta2.php" method="post">

<table border="0">
<tr>
<td>Nombre</td>
<td><input type="text" name="nombre" size="30" maxlength="30" /></td>
</tr>
<tr>
<td>Web</td>
<td><input type="text" name="web" size="30" maxlength="30" /></td>
</tr>
<tr>
<td>Telef</td>
<td><input type="text" name="telef" size="20" maxlength="20" /></td>
</tr>
<tr>
<td>Sector</td>
<td><input type="text" name="sector" size="30" maxlength="30" /></td>
</tr>
<tr>
<td>Descrip</td>
<td><input type="text" name="descrip" size="50" maxlength="50" /></td>
</tr>
<tr>
<td>Karma</td>
<td><input type="text" name="karma" size="3" maxlength="3" /></td>
</tr>
</table>

<input type="submit" value="aceptar" />
</form>

<?php

$link = mysql_connect('localhost','usuario','contraseña');
if(!$link){
die("Not connected :".mysql_error());
}

$db_selected = mysql_select_db('buscador',$link);
if(!$db_selectd){
die('Can\'t use buscador: '.mysql_error());
}

$nombre = $_POST['nombre'];$web = $_POST['web'];$telef = $_POST['telef'];$sector = $_POST['sector'];$descrip = $_POST['descrip'];
$karma = $_POST['karma'];

$consulta1 = "INSERT INTO empresas (nombre, web, telef, sector, descrip, karma)";
$consulta2 = " VALUES ('".$nombre."', '".$web."', '".$telef."', '".$sector."', '".$descrip."', '".$karma."')";
$consulta = $consulta1.$consulta2;

mysql_query($consulta,$link);

mysql_close($link);
?>

Notice: Undefined variable: db_selectd in C:\xampp\htdocs\Pruebas\alta2.php on line 16
Can't use buscador: