Definitely get a Mig - Gas over gasless every time, the weld is much cleaner (gasless is nice in the wind, but not tidy!!)
150amp is great for a learner, any bigger and people tend to get frustrated and turn them up, increasing their problems (and frustration) - anything less that 130amp wont have the power for "big" welds.
Make sure it is a "Turbo" (means it is fan cooled) - gives a longer duty cycle (the time before it gets too hot and shuts off - being an IT Guy, you'll know that!)
Dials are better then Hi/Lo switches - as others state gives better control.
A working second-hand MIG is usually good value for a novice (although I always buy second hand machinery like this - but also enjoy fixing all types of machinery up as well as using them....). If buying second hand, make sure you also buy a new gun-liner (little plastic tube that the welding wire runs through), compatible wire nozzles (for the wire size you are using) and a new gas shroud. these items are really cheap - and many times ive used other peoples welders where these items are worn/damaged....and they wonder why "the welder" wont weld "properly...."
The guys on here are really helpful - with some immense fabrication experience - check out some of the resto/build threads and see what can be done, you can do it too!