Xp Running Out Of Resources

running xp sp2 on a dell inspiron 9300, xp sometimes starts to lose resources, failing to open new applications, new explorer windows or lacking parts of guis in applications, such as explorer button bars or parts of menues. but if i then close an already open application to free some ressources and repeat the action that failed (e.g. opening a new explorer window) xp might be able to do it properly. i can repeat this a couple of times, until i'm down at only a minimal number of windows/apps and will have to reboot. after reboot, everything is normal again.

here's some more examples of strange things i've seen:

- explorer windows won't open at all, no error msg, system sometimes 'beeps'

- an explorer window might not display the buttons-area under the menu, but only a windows-logo in the center.

- an explorer window might display without the task area (blue area) that's usually on the left side

- whole applications won't start, sometimes giving error messages, sometimes not

there is no consistant error message that would identify which resource type the system is running out on. the system is constantly scanned for viruses, trojans, et. al. using symantec antivirus and hijackthis. there is more than enough memory (2gig) and taskman will display enough free memory when i encounter those situations. the system is used daily (sleep mode at night, no hibernation) and the problem might show up after 3 days or only after 3 weeks.i first suspected photoshop and dreamweaver to mess up something when running in parallel, because the problem always showed up shortly after those two apps had been run together. i stopped doing that, and found that it still happens, but it will just take longer.