Building PC's is not as difficult as it sounds, but I must say, don't buy parts and import unless you are sure because it could be different connectors, incompatable, wrong voltage, etc...
Also your warranty would be difficult on any componet.
I would suggest taking a look at click here or click here
They both are decent prices, have a look for compatable componets, bundles are sometimes good, and make sure your motherboard has a Building a PC guide, I know for sure the Gigabyte GA-7VAXP one does, this will take you through all the steps.
You will need all the required componets. Processor, motherboard, Drives, modem (or netowrk card for broadband), Graphics and sound (Sometimes on-board). And a screen along with a good old floppy.
Choose your spec carefully! What do you want your PC to do?
A. Internet, Typing, etc
B. DVD, CD-RW, Internet, Photos, Odd game
C. Games, CD-RW, DVD, Photo editing & Video editing.
If you choose mostly:
A. A basic PC with about 1Ghz to 1.8Ghz
B. You need a Fmaily PC with 1.8Ghz to 2.6Ghz
C. You need a power PC with at least 2.6Ghz or more.
Hope this helps, and if you need any more help give click here ago or click the mail button by my name to e-mail me.