Have you tried the above?
IMO...those insufficient resources messages can be an awful lot of factors. I found an old BC thread about such...you will note all the different ideas that popped up, http://www.bleepingcomputer.com/forums/topic49537.html
You could have more RAM...but that system would be pressed for resources only if you are running heavy-duty programs like Office, Adobe, etc.
I would look at two things initially, after checking the Dell link above.
a. Check that XP is managing virtual memory.
b. Take a look at programs installed and uninstall anything that you don' t really need. As a corollary of that, I would take a look at the items running at startup and eliminate anything but the most basic.
I believe the programs installed and running...offer the greatest chance of resolving this particular error.