Got Some Mac Questions

I have a Gateway 19" wide screen and I love it but I'm always wishing for more space, ya know? And my current computer has been having huge problems lately, its just getting a bit to old. It can't run good ole Counter Strike 1.6 without freezing. So to cure that I put a box fan right next to my case with the side panel up and it holds up for the most part.

But now I want to get a new computer. I'm 75% leaning towards taking my web ventures to the next level (college and above), and everywhere I've been told is that I need to get accustomed to a Mac. Budget wise I guess I'll spend around $2500 and just pay it off monthly so I don't spend all of that money at once. I just don't know what to get.

I'm thinking about either the 20", 24" iMac, or the Mac Pro (baseline with maybe the 2GB ram upgrade). Can anybody provide some suggestions? I'll going to run Windows so I can still game from time to time, but I really want a more reliable computer that doesn't crap out on me. And this current one takes a long time to boot up and open applications. Pretty soon I won't be able to run the latest software. Anyways here are my current specs:

AMD Athlon XP 2500+
1GB of crappy ram
GeForce 6800 LE

And well I'm having a hard time choosing between the:
20" iMac
24" iMac
Mac Pro

Could anybody provide some suggestions?

You should get a Mac Pro.

Yea but for the same price I can get a nice 24" iMac with 2GB of ram and a 7600GT. Decisions decisions...