Moving the swap file to a different physical hard drive can only
improve performance if Windows is actively using the swap file; which
means that it is frequently moving less active memory pages from RAM
to the swap/paging file and then moving these pages back into RAM
again later when they are needed (and after also moving something esle
from RAM to the swap file to free up space to load them back into
RAM).
And if Windows is actually doing this then adding additional RAM will
probably cost less than the added hard drive, and the performance
benefits will be far far greater.
For more information about virtual memory management in Windows XP see
the article by the late Alex Nichol MVP at
http://aumha.org/win5/a/xpvm.htm
Good luck
Ron Martell Duncan B.C. Canada