Adding more memory can noticeably improve performance only if the
added memory results in reduced usage of the virtual memory paging
file.  Therefore if the paging file is not currently being used to any
significant extent then adding more memory will not provide a
significant improvement.

Unfortunately there is no ready way of determing actual paging file
usage provided with Windows XP - it does not have an equivalent to the
'Memory Manager - Swap File In Use" reporting provided by the System
Monitor utility in Windows 95/98/Me.

There is a free utility that you can download and run which will
provide this information for you. It was written by MVP Bill James and
you can get if from
http://www.dougknox.com/xp/utils/xp_pagefilemon.htm or from
http://billsway.com/notes_public/WinXP_Tweaks/

If that utility shows actual page file usage of 50 mb or more on a
regular basis then that is indicative of fairly significant paging
file activity. Adding more RAM will reduce or even eliminate entirely
this activity thereby improving performance.

This apples regardless of how much or how little RAM is currently
installed in the computer, at least up to the 4 gb RAM maximum for
Windows XP.

Good luck

Ron Martell     Duncan B.C.    Canada