when you want to take a pic in game u press f9. Well, that is the button by default. If you have something else there than i dont know. after u take the photo it should be in the system folder of the ut2003 folder. It will be a bitmap (.bmp) format picture. To post the pictures on the internet you need a file converter: http://gms.cyberrock.net/DownloadCenter?UTScreenCaptureConverter
After you download it, simply place the file in your system folder and open it to convert all your pics... BTW if you cant open it than you need to download winrar: http://www.download.com/WinRAR/3000-2250_4-10745708.html?tag=lst-1