gseaman I read that Linux is more supportive of nVidia graphics cards.
Still not sure I want to build another one or just buy one.
Pardon if I just jump in here. nVidia graphics are well supported in Linux, as are ATI/AMD and Intel. Of the first two, I tend to favor nVidia over ATI/AMD, but that's changing - AMD is doing some really neat things lately. In actual practice, I own more Intel video hardware than anything else (unless we're talkin' antiques here - I still have cards made by Cirrus, Chips & Technologies, Diamond, and S3 laying around somewhere...) I tend to build for reliability.
As far as build vs. buy, economics is now in favor of buy, so if money's tight, that's the way to go. That said, nothing beats the satisfaction of knowing every nut, bolt and screw on your hardware, and that comes with a good build. When I buy computers, I generally wind up inside the guts inside of the warranty period, anyway, but I still buy more than I build nowadays, and I advocate the use of refurbished hardware - sure, it's a generation or two behind, but it's cheap, generally proven to perform well when carefully selected, and durable, especially refurbished workstations (I tend to favor the Dell Precision Workstation line for refurbs).
One thing,though: I don't buy refurbs with much of an eye toward upgrading more than maybe a hard drive. RAM for workstations tends to be the more expensive "server" stuff (ECC Registered RAM), and I usually just buy (or trade for) a machine with enough RAM already installed.
If you decide to build, do your research. The field is constantly changing, and new stuff is coming out all the time. A really snazzy case may be passed up by an even better design that you might like more if you keep looking. Read reviews, and tweak your BS filter up a notch or two when you do.
You're right on with your earlier comment on power supplies. I've lately favored Antec supplies as being very conservatively rated, but Compucase HEC and Thermaltake are good units, too. PC Power & Cooling was recently acquired by the OCZ Technology group, and that's probably a good thing - they generally produce the Cadillac of power supply units, but all things for a price, effendi.
Good luck in your endeavors, whichever way you decide to go.