I was having a problem last week at work. AdAware didn't stop it. I used task manager to show the currently active processes. I THOUGHT there was some way to get basic info on each process (maybe there is, I'm using XP at home and W2K at work). Maybe I searched for the Image Name of the process to see the folder tree it was in; sorry, I don't remember. Anyway, once I eliminated the ones I knew and the ones from Microsoft there was only one process left. So I ended the process and moved the .exe to my desktop and restarted. The pop ups stopped. So I trashed the .exe.
If you try this, be EXTREMELY careful! Don't just go randomly ending processes. There are places like BlackViper.com which can identify many of the services and what they do. I only went through with it because when I found and right-clicked on the .exe and chose properties, the name or company or some bit in the versions tab said something about ads or ad-creation, so I was pretty sure I had the right program.
Good luck with your problem.