Here is how to increase your virtual memory on Windows XP, but please note that the more you increase it, the more it takes away from your hard drive storage memory:

1. Click Start, click Run, type sysdm.cpl in the Open box, and then press ENTER.
2. Click the Advanced tab, and then under Performance click Settings.
3. Click the Advanced tab, and then under Virtual memory click Change.
4. Under Drive [Volume Label], click the drive that contains the paging file that you want to change.
5. Under Paging file size for selected drive, click Custom size, type a new paging file size in megabytes (MB) in the Initial size (MB) or Maximum size (MB) box, and then click Set.
6. Click OK to close the dialog box and apply changes.

If you want to upgrade the actual  physical RAM memory inside of your computer, which is the best thing to do in my opinion, we have a great tutorial for that here.