Since spybot is free there isn't any harm in trying it. Webroots spyware sweeper seems to have promising report when I googled for it, but like I said you've got nothing to loose.
Have you tried running a virus scanner? you can get a free one from www.grisoft.com
Firefox is a web browser, you can find out more at www.mozilla.com
. It's uniquly different from IE and less suceptable to attacks and popups because it has a good popup blocker built into it.
I think it's most likely there is a program installed on your PC that is getting these popup ads for you, so switching browsers will not fix this problem, but it *might* help prevent future problems.