Oh My!

So I just got back from Comp USA. I checked out the iMac 24 inch and wow, was I impressed. Mostly with the screen though. It was gorgeous, and the size was monstrous. I really liked how clean everything was as well. I've got a few questions for the hardcore Mac guys though, so here we go.

Gaming: I read a review that places the iMac at around 80-90 frames per second on 1024x768 on Doom 3. Overall, does this sound pretty respectable? Is the supplied 7300gt graphics card any good, or is it imperative that I upgrade? Right now, I love playing older games like Diablo 2 and Counter Strike CZ & 1.6. I'm sure the base model will be adequate for those games, but what about future releases?

Memory: Is 1GB adequate for a Mac? Or is it recommended to upgrade? Not really sure if I should go for the 2GB upgrade, but no way in hell am I going to pay $500 for 3GB of ram.

Financing: Can anybody summarize how the Apple Financing plan works, or does anybody have a link that explains it in plain English rather than the Apple.com store? I'd really appreciate it.

If you haven't looked at the 24 inch iMac in person, I highly recommend it. Its a gorgeous computer.