Setting your Windows XP pagefile (swapfile) to an arbitrary multiple of your physical memory amount is often recommended, but is not the best practice. It's a kind of geek urban legend.
It's great that people offer helpful advice like this, but unhappily it's also quite easy to spread advice which is not the best, with the best of intensions.

For an expert discussion of Virtual Memory and and best practices, see:
WinXP Virtual Memory

I'm a PC consultant, as well as a 3D graphics writer and web services guy. My free PDF brief on setting up and maintaining a Windows XP PC is at:
Free Windows XP setup/maintainence brief, in PDF format

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