If you have WinXP and any sort of background processes, then 256MB is probably at bit on the weak side. You really do not want to go into using Virtual memory, as this usually slows things down quite a bit.
I recommend a minimum of 512MB RAM for almost all XP machines.
Ctrl, Alt, Del, Task Manager, look at the Performace Tab and see what the Memory Graph indicates, post this info back. Look at the bottom left of the Task Manager for the number of operational processes, anything over about 45 is probably tasking your 256MB of RAM, post back the number of Processes.
Run the Check My Computer utility for info on what RAM your machine will support and what the pricing is:
Check My Computer
JamesO