well, I'm getting a pretty good deal from my local shop since I used to work there and know the guy who owns it pretty well. Not to mention warranty. And if it breaks, I have help right down the street.

and yes, chances are if I try to build it even with a guide, I will mess something up. I know this because I once rebuilt an old PC with someone checking up on me every so often and still managed to mess something up, and I still don't know what it was.
I could probably build one decently, but if i spend the extra money I can have someone else do it right the first time, and have them fix it for free if they do it wrong.