what he said: there may be spyware and other stupid program running on your machine...
some ways to do it:
- repair msie (start > setting > control panel > add/remove program > msie > repair)
- go to regedit and edit
HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Main\Start Page from that stupid website to whatever you want
- install and use different browser
- format (ok, maybe not that bad, but hey ---

)
also, next time you should try avoiding that website ... what was it about anyway? (don't feel like going there to find out)
good luck

-986-