The virtual memory on your computer should be adjusted to provide optimum performance, and minimum fragmentation. While this guide is written for Windows XP, the changes and settings are also fully applicable to other Windows operating system (however the locations of the menus in question may be different).
To properly adjust your virtual memory, you need to know how much physical memory, or RAM, is on the system. You can find this by going to Start-> All Programs-> Accessories-> System Tools-> System Information. Within the System Summary section of the system information window, find the Total Physical Memory. This is your RAM.
You should change the virtual memory to (A) have the same Initial and Maximum size, and (B) set this size to be 1.5-2.5 times the amount of RAM on the system, depending on your hard drive space requirements . You can do this by going to Control Panel -> System -> Advanced tab -> in the Performance section click Settings -> Advanced tab -> in the Virtual Memory section click Change.
It is not advisable to let the system automatically control the virtual memory, so to override this, choose the Custom Size radio button. You can then manually adjust the values. Once you have changed the values, click the Set button to save the changes, and pick OK. You will then need to restart your system.
In order get the full effect of this change, it is strongly advised to defragment the hard drive several times in a row. This can be found via Start -> All Programs -> Accessories -> System Tools -> Disk Defragmenter.