GD installation prob

I'm running PHP 4.3.1 on WinXP and am trying to use the GD library, which I understand is installed as standard in that release. The problem is that when I use a function like imagecreatefrompng I get a fatal error - call to undefined function. I looked at PHP.INI and found that the php_gd.dll and php_gd2.dll extensions are commented out and the extension_dir set to ./ I tried uncommenting the GD dll files and set a path to where those files are on my hard drive. But when I restarted, PHP went haywire complaining that these functions were already defined thanks very much. Any thoughts? (The code I wrote (sort of) works on my hosting system).