If all else fails, use
Google. I use google all the time when I have tech problems, don't understand something, or just searching for stuff. I believe that Google is one of the best websites ever created.
Anyways, here are some that you'll need:
Videocard (The type depends on what you are gonna use the comp for. If it's for gaming, I'd go with a 128bit or a 256bit. Otherwise an old 32bit or 64bit will work fine)
Soundcard
Processor (not sure, but I think it comes on the motherboard. If it doesn't then I recommend a 1gHrz or more)
Fan (maybe)
Hard disk drive (anything from 40gig+ is normally good. Once again, depends on what you wanna use it for.)
RAM (This allows you to store a lot of things while the computer is on. I believe 510 is a good amount, but I believe 256 would work fine.)
That's all I can think of. I personally wish my comp was as good as some of the stuff I put down.