google:
''build your own pc''
Search CNet forums:
''build your own''
The first thing you need to ask yourself is how you will use the computer. Gaming, high-end gaming, video editing, graphic design, programming, word processing browsing and email, general use, accounting, CAD, etc. That will lead you to a CPU choice. Everything will start to fall into place when you search for a motherboard that is compatible with your CPU.
If you have never even upgraded a PC before, you need to do a little reading. You can do this online or get a book like this one:
http://www.dummies.com/WileyCDA/DummiesTitle/productCd-0471767727.html
(No insult intended with the ''Dummies'' book. They are fantastic resources.)
If you want recommendations for websites that have good step-by-step instructions on what to do, I strongly suggest creating a new discussion (the green button), rather than burying that request in this discussion about hard drives. You will get a lot of suggestions. Make sure you post what you want to be able to do with your new computer.
Hope this helps.