Topshare replaces IE page

I have a Dell PC running XP SP3 on a DSL line, and evertime I bring up IE it gets replaced by another IE window saying if you go to this site there is spyware there. I click the more information button inside this window and it wants you to purchase their spyware software for $49.99. The software is called "Magic Software" from "Magic Software, Inc" which is part of a company named Topshare out of "AU". I have run norton anti-virus, spybot, and I installed CCleaner last night and ran every part of it (all of this was run in normal verus Safe mode). I have tried to read the links about various malware, but it leads down too many trails. Is their a shorter fix to rid myself of this?

Thanks
wbaria