Firefox, Internet Explorer and Ping

I have a pc with XP sp2 isntalled that can browse the internet with no problem using the firefox browser. Internet explorer will work for a while then it stops working at different times. When it stops working I can STILL browse using firefox and of course I can still ping websites but Outlook 2003 also stops working when I am having this problem with IE. Only after I reboot will this problem be temporarily fixed until a few hours later another incident. I reboot everyday and have all the latest updates, cleaned out all cache & temp files. Does anyone have a fix for &/or know whats going on?