Well ya system is faster than mine i gotta say, and I don't see why your system is going so slow though. I have myself a 2000XP, 512 DDR266, Geforce 4 Ti4200, KT600 motherboard and i haven't found a game yet i can't play at super resolution. Saying that, if your playing with 64 bots as u say in your post, it probably explains your performace. I don't think any processor could deal with this amount of work to do to be honest ! perhaps you should play online !
As for upgrading to 64 bit, as u say, you will need new mobo, CPU and memory. I would save up, and wait until end of year when Windows 64bit is out, and Socket 939 is readily availible to consumers.