Messenger Sevice pop-up Ads

Hello;
I've been trying to find a way to get rid of these 'Messenger Sevice' pop-up ads that are appearing on my computer and haven't had much luck. I assume that some Adware has been installed onto my 'shared' computer and was hoping to find a way to get rid of it. The ads are popping up in a overlay format similar to the 'netsend' messages and when I click on the 'Go To Process' in the Applications section of the Windows Task Manager, it highlights a file called 'csrss.exe'. I know that this file is used for the console (text) windows and process management.
All said, is there any way to remove these annoying ad pop-ups??? It's quite frustrating to lose your Hardcore character in Diablo 2 because some stupid ad is advertising me "Another 2 inches to your penis in 3 hours!!!" as it mimizes my game to the Desktop and my character gets wiped out.

Specs:
OS: Win XP
Firewall: Sygate Personal Firewall
Virus Checker: Norton's
Other applications usually running: MSN Messenger, QuickTime, Epson Printer stuff

Any help would be greatly appreciated.
Thanks!

Thanks! Greatly appreciated.