I don't know about XP specifically, even though I use it, but with all other OS's from Microshaft, the optimal swap file size is twice your amount of RAM plus 12. An example, if you have 512K RAM, your swap file should be 1036K. The reason for this is that the OS will never use anything more than that, and it is the OS that controls the swap file. This is from Microsoft's engineers and programmers off the record. On the record, they say use the setting that allows the OS to manage it. (They don't). Virtual memory and swap file are the same thing. The only real reason to set it to a fixed amount is to prevent fragmentation, thereby slowing the computer down a little. If you want to tweak the OS to the utmost ultimate speed in regards to virtual memory, then you would place the swap file in it's own dedicated partition as the first partition on the fastest hard drive you have.