I bought a full-size chassis when I built my current system, because I've got big hands and was sick and tired (after three self-builds) of scraping my knuckles on sharp edges and having to remove components such as the CPU fan just to get other ones in or out.  I have to say, having all that room to work in is an absolute luxury.  I got the self-build bug, particularly when it came to CPU coolers, thermal paste and operating temperatures. 

If you can make use of any advice: the stock coolers that Intel supply work just fine, and are quiet, but they can be an absolute pig to seat properly and to lock down; Zalman do a good range, and I currently have a CoolerMaster one.  All of these have far simpler, and more effective and secure mounting systems than the CPU manufacturer's versions I've seen.  Also, it's easy to get obsessed with thermal paste!  The best tip I could pass on is to realise that you're not icing a cake - drop a small blob of it in the centre of your CPU, and it will spread out just fine under the pressure of the fan mounting clamps/screws/whatever.

My systems that I have built have all been Socket 775/Intel setups; I would never again buy a ready-made system from a retailer. 

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-----!"