Internet Explorer Process still running

Happy New Year Everyone. I’m having a problem with my works Dell PC. (2.8 P4, 512 RAM, WinXP PRO, Networked, NAV). I discovered that after I close Internet Explorer, the process is left still running (approx 25,000k). I discovered this when my machine went slow, and wouldn’t even open up IE. At the moment, I’m having to close IE, then [ctrl][Alt][Del] to Task Manger, and end the process from there (as many as incidents if IE, I’ve had running). I’ve checked for all the usual suspects, such as spyware, viruses, etc. Anybody know why this is happening, or more to the point, how to fix it, please