Gads Emelius....
Since you can only go to 128MB RAM for gaming, then you really need a new computer (not a CPU upgrade) to handle the current games.
I haven't been able to go and check with Circuit City , but according to Fshrking the Emachine T3256, with monitor and canon printer can be had for $370 (don't know how long).
http://reviews.cnet.com/5208-6121-0.html?forumID=45&threadID=55529&messageID=699873
Rush yo little butt down there and buy one for that price. If you already have a monitor & printer, your can advertise & sell them real cheap to further bring this new PC to around $250 or less. You can use or sell your current machine for just basic net roaming and simple gaming. Heck , I'm temped to buy a T3256 even tho I have 3 good computers and dont't need another...by far.
Take a look at the Emachine T3256:
The basics: AMD Athlon? XP processor 3200+ (2.2GHz), 512MB RAM, 160GB hard drive(7200R RPM).
DVD+/-RW and CD-ROM drive: Back up documents and burn multimedia projects to CD or DVD. Use the extra CD-ROM drive to play audio CDs or run other software.
Ports: You get plenty ways to add peripherals, including 5 USB 2.0 ports.
8-in-1 media reader: If your family has digital cameras or other memory-card devices, they can transfer files using the built-in 8-in-1 media reader. Accepts USB 2.0, Compact Flash I/II, SmartMedia, Memory Stick