Can't get extension dlls loaded in Windows

I'm using Omnihttpd Pro personal web server running on Windows ME, and with PHP 4 bundled with the server. When I try to enable dlls by uncommenting lines in php.ini (e.g. ;extension=php_gd.dll) the browser becomes unable to load pages from the server, takes a long time trying and then gives up with a blank page showing. I've left the extension directory at the default of "extension_dir = ./ " with the dlls directly under the php directory. I've a copy of php.ini in both the php directory and under windows, though its the latter thats being read. Any suggestions please - I really want to use the gd extension!! (Note I get the same problem if I uncomment any other dll lines in php.ini) Alan Hale