Couple of suggestions.
Check to make sure you have the latest drivers for your video and sound card, as well as the motherboard. Since you have a Dell, their website SHOULD have them. If not, call tech support.
Open up your device manager and make sure there are no conflicting devices. If so, call tech support and let them help you sort it out.
Lastly, try running Firefox as your web browser.
www.mozilla.com/firefox
Did your computer come with the Windows XP already installed, or did you have to put it on there yourself. If its the latter case, its always a good idea to "burn in" the system for a day or so before installing any additional programs.