Build or buy?

So I'm sure questions like this get asked quite frequently -- I apologize in advance.
I am still using my 5 year old eMachine for gaming/ music production/ general use but I have recently come into some money. I figure now is as good a time as ever to upgrade. My budget is set at around $1000-1200. I am very interested in future proofing my computer as best I can because, as you can see, I do not upgrade my system very often. Naturally I am interested in the i7 line of CPUs and Vista 64-bit. At the moment I have my eyes set on http://www.newegg.com/Product/Prod [...] 6883229092 as it seems to have everything that I would want/need. Any time that I try and build a system on newegg the price of the components comes out higher than that of this pre-built one. Anyway right now I feel like I am leaning towards the pre-built system as I have never actually assembled one myself. However, if I stand to save significant money from building a comparable system myself I would b open to it. Recommendations?

1. future-proof computers?? I have yet to see one.
2. Self-built PC always cost less then pre-built. You may be looking at newegg parts that are of higher quality then the pre-built PC.
3. self-built PC is always easier to upgrade then pre-builts but they obviously lack the warranty so each has their own pros and cons.

If you can build a pc (which most anyone can with some reading) always do it. it will always save you money, its easier to upgrade, and that knowledge is great to have.