How much free hard drive space do you have?
You might not need a new system yet. I guess that depends on what games you play, or want to play, though.
AOK doesn't really need that much. You could probably be able to hold out for a little longer with just a RAM upgrade (you haven't replied with it yet), and a decent Internet connection (you have cable, so you're good) if the only game you're playing is AOK.
You could then get another computer when the prices drop a little more. Recently I've seen complete XP2100 machines for around $280. But anyway, there are a lot of options for around $300 that are pretty good. Just wait a while until after you get your car. Then you can get a new computer, and set up a nice little network.
Btw, don't get a laptop unless you absolutely need the portability. They don't last as long as desktops (average life is around 3 years because of all the lugging around), and since you'll be paying about 4 times the amount for a laptop as you would a desktop, it's not really worth it.