|If you need to reset the size of your pagefile (also called your virtual memory):|
Right click on 'My Computer'>Properties>(I do not have XP anymore, but I believe that you need to look under the advanced tab) and look for a button that says 'virtual memory' or 'manage virtual memory', select this and a new box will pop up allowing you to set your virtual memory size (pagefile) for each drive you have. Generally leave it on 'allow windows to manage your virtual memory'. If you need specific recommendations for settings to solve a specific problem, post back your needs and system spec's (including RAM size) for advice (I will warn you that you will probably get some conflicting advice from different people as opinions vary).
You have to be a little bit crazy to keep you from going insane.
If all else fails, read instructions.