Go to Start/Control Panel/Systems, go to the tab Advanced, then click on Performance Options. In there you will find Virtual Memory with a button Change. Click on that.
Then set the Initial Size and Maximum Size both to the same value of 1.5x your PCs amount of memory. If you have 512MB, set it to 768MB. Then click the button Set.
You will probably have to reboot.
Your pagefile is too small, rather than too large.
These instructions pertain to Windows 2000, but I assume XP will have the same.
Next time, please give us some more information about your system.