Power Scan Spyware

This is a nasty spyware. My e-mails all go through Mailwasher before I open them, my ISP checks for viruses and has spyware and pop up protection. I also have Norton. Somehow this spyware still got through and is a pain in the neck.
Just about every time I click on something a large popup displays ads.
Today when I went to Google to find something this spyware covered the Google page with it's own search page.
Earthlink my ISP says it's catagory is Adware and it is an applet loaded by toolbar drive-by's(I have no idea what this means).
It's a software application that installs itself on your computer and displays advertisements and there is no means of uninstalling it.
Am I doomed to live with all these popups or is there a way to safely get rid of it.