error loading dll

Hello, I have a strange problem with PHP4.03pl1 (CGI mode) under WinNT/IIS4: I put a "extension=ms_sql70.dll" in php.ini, but get an error when trying to load this dll (e.g. by doing a phpinfo()): error loading my_sql70.dll - module cannot be found. I tried setting extension_dir, I put the DLL into the system32 directory of Windows, but no avail. Even if I supply the full path to the dll, it always says error loading c:\path\to\dll\ms_sql70.dll - although c:\path\to\dll\ms_sql70.dll does exist. Any ideas? Regards Christian