Check the vulnerability of your PC's ports here
GRC|Gibson Research Corporation Home Page Scroll down to HOT SPOTS & choose ShieldsUP! In the light blue window click on "all service ports". The vulnerability of your baby will be tested.
If you have the time, read through the sight, seems like they know what they're doing.
I'm running Firefox 3.5 under Windows XP pro SP3 & none of my ports are detectable, stealth mode, I came to learn.
Edited to add : I've always run as Admin (single user) and have never had any problems.