A couple of questions to ask yourself on the build or buy dilemma can help narrow it down for you.
1. What, if any slavageable hardware do you have in your existing computer? Is the DVD burner SATA? if not, scrap it, a new sata one is $20. How big are the hard drives? Under 250gb, probably better to buy new 250gb for $40, how old are the hard drives? if older than 3 years, new drives are the way to go, as drives last 5 years on average. Is your case equipped with 120mm fans, or smaller noisy 80mm fans? if it has 120mm, that will save you $80.
2. What is your skill level. Are you interested in building a computer, and do you have someone local to help you with any of the tricky things if you have never built one before? Or do you consider it a hassle, and are only considering it to save money, or to end up with a better machine than you can buy? If building a computer isn't something you personally want to do, buying may be the way to go.
3. Whats your budget look like realistically? For $1,000 you can build a pretty decent midrange gaming PC. For $1,500 you can build a solid state drive, 580 GTX equipped monster PC. You can probably buy a mid range PC for $900 ish or so, and get a bit better warranty support. A high end purchased computer will start at at least $2,200 for the same thing you can build. If you are looking to get a high end machine, it makes sense to build your own. Also if you are looking for a machine that you can upgrade, rather than buying a complete new one in a few years.
If you give me an approximate budget number to play with, I can write up a potential build for you to look over, and find some comparison PC's for purchase to give you an idea of where you would be at for each of them .
Admin edit: also, your sig is really, really long. Please shorten it by about half...
Edited, Jul 26th 2011 11:17pm by Kaolian