You CAN increase the virtual memory size. This is in XP:
1. Click Start, then open the Control Panel.
2. Click System.
3. Click the Advanced tab.
4. Under Performance, click Settings.
5. Click the Advanced tab.
6. Under Virtual memory, click Change.
7. Under Drive [Volume Label], click the drive that contains the paging file (virtual memory) settings that you want to change. In almost every case, this will be your C: drive.
8. Click to select the "Custom size" option, set your values, then click Set.
9. Click OK three times and restart your computer.
I recommend setting the initial size about 1.5 of the amount of your RAM (say you have 1 gig RAM - set it to 1.5 gigs) and setting the maximum size about two times bigger than the initial size (initial is 1.5 gigs - maximum is 3 gigs).
And this is why you should ALWAYS have free space on that drive.
Hope this helps.