If you are going to buy a welder, my Miller...period...maybe a Lincoln (mig only) if you find a good price on em... here is a good site for welding stuff online, they have some of the cheapest prices around:
www.cyberweld.com
As far as MIG and TIG go ... MIG has just a one piece torch, the wire comes out of the middle of the torch, its easy to weld, but harder to see the weld puddle and harder to be real accurate and clean with. That said, a little 110 amp Miller or Lincoln MIG will do about anything you will need to do on a car. But I do recommend getting one that you can hook up a gas line to cause it welds TONS better with Gas than with flux wire=very messy.
TIG is basically the same as Oxy fuel welding, except alot cleaner and alot more controlable ... with TIG you have a torch that supplies the heat, then you hold the filler rod in you other hand and feed it in as needed, and the best part is you have amperage control either with a foot pedal or a knob on the torch that allows you to weld hotter or colder as you go, so you can control the weld puddle and set your pace better.
Anyway, I just got a Miller 250 Tigrunner ... it kicks ass!!! But probably a litte more than most want to spend on a welder. 914 rust...here I come
Tony