I've put bikes together before (I currently own a 2002 Lemond Poprad) and have a fair few tools, although I may need a hand from a local shop getting the disc brakes right (not squealing in other words!).
Thing is I'm just not that familiar with Mountain bike frames and components so can't look at the set up of the Nashbar at-2 and say this is a good deal or this is not worth the money. If I had $500 right now I'd get something like a GT Avalanche 3.0, but I don't. I figured I could get an at-2 for something like $275 with the right coupons then upgrade the components (brakes, wheels) in the future if I really get into Mountain biking (in other words if I have time - I have 2 young kids!).