I spent a decade or more getting ripped off every few years by a major PC retail chain here in the UK until a few years ago I actually summoned up the courage to look inside the box of the latest PC to fail.  Once I had worked out that there are only seven or so individual components, I took the plunge and built my first PC; I have never looked back since. 

The word really needs spreading about how easy, satisfying and above all cheap it is to do it yourself - if the general public knew I doubt anyone would buy off the shelf PCs again....

Ashley is right - the key is the motherboard, everything else really stems from that, and the OS you want to run.  You can never do too much research before buying, either!

Good luck and happy rendering!

My self-build system - Vista 64 on a Kingston 240GB SSD, Asus P5Q Pro MB, Quad 6600 CPU, 8 Gb Geil Black Dragon Ram, CoolerMaster HAF932 full tower chassis, EVGA Geforce GTX 750Ti Superclocked 2 Gb, Coolermaster V8 CPU aircooler, Enermax 600W Modular PSU, 240Gb SSD, 2Tb HDD storage, 28" LCD monitor, and more red LEDs than a grown man really needs.....I built it in 2008 and can't afford a new one, yet.....!

My Software - Poser Pro 2012, Photoshop, Bryce 6 and Borderlands......"Catch a  r--i---d-----e-----!"