GD instalation with omnihttpd under win98

I tried to use GD dll with php 4. I did that by downloading the newest binary distribution then edited the php.ini file. There I've set the extension_dir = "c:\programme\httpd\php\dll" (should be the right path) and then put the ; away before ;extension=php_gd.dll, but every time I try to execute any php file with this php.ini it doesn't, even with a php file that only contains <? echo "hello world"; ?> and every script works again, as soon I put the ; again in front of the extension tag! Can anyone tell me what I did wrong or what else I have to do, to generally be able to use extensions? Thanks a lot