Boy, that didn't take long... "adware" is also called "spyware", btw.
Here's a link to a freeware utility to remove adware. From your brief description, not sure if it will fix your problem, but it sounds like good software to have just in case (sort of like a virus detector).
Haven't used this particular bit of software myself, but from the description it seems very complete.
Thanks, but it isn't that... It isn't directing me to good sites from advertisers, like popups... I am redirected to broken and non-existent sites... 404 errors... A click to Preview this response may take me to a 404 "Page Not Available" page at USA Today or Webshots or TORN or The New York Times...
I don't have any of the spyware/adware stuff on my machine... It is clean.
I had one virus before upgrading to XP and IE 6, but this was not described in it's list of damages (it was one of the worms that attacked instant messengers), and I have since then always kept PC-Cillan up to date.