When you boot your machine, Windows creates a special file - the swap file - on your hard drive.

Windows uses that file as auxiliary memory, temporarily storing in there stuff it does not immediately need to do its work.

Windows' reliance on the swap file is increased when you don't have enough physical memory, or random access memory. That is especially true if you are dealing with very large files -- such as those with photographs -- and if you have a lot of programs loaded into memory.

Although XP can and does increase virtual memory by creating a large swap file on the fly, the best solution is to add physical memory to the PC. These days 512 megs is the ideal.