Extensions load errors

Hi, I'm trying to get extensions to load on my w2k, apache 1.3.x, php 4.0.6 cgi installation. Everything seems to work fine up to the point I uncomment :extension=extension_name. I've added a IUSR_machinename and given it write permission to the dll dir. I've copied dlls to the php.exe dir and changed the extension_dir to c:\php but still can't get any extensions to load. Apache reports the "procedure could not be found" Any ideas? I'm new to webservers and php so I'm probably missing the obvious. Thanks, Steve