Not enough memory to run......

Last night I was on here and all I had open was internet explorer. All of the suden I get an error that there wasn't enough memory to run. I did control, alt, del, and gradually one by one closed out on everything except systray and explorer to see what was using the memory. It never did go down. I ended up restarting. At the time I got the error message I still had 70 some percent user resources, so what is up with this? On my old system I would get that message every now and then, but it was only 64 mb, this is 128. Should I have gotten more memory or something? I have had it a month and have had no problems with it and have not froze up once. It is a 4100 series, 866 processor with the 815e chipset. I have gone to denny's site and done msconfig. Is there anything else I can do to lower te memory usage. Right now I am using 83% as I am on here. Feel free to email me also if you have ideas. Thank you!

Laurel