Prophet

I had to reinstall windows xp on a pc the other day and after running windows update IE8 locked the search provider to bing. Under manage search providers I was unable to change the default search from bing. I was unable to uncheck the box allowing programs to suggest changes to my default search engine.
I repair pcs from my home and on this particular day I was working on someone else's pc. I had to hold pc for an extra day and redo OS again to rectify issue. I haven't had time to see if there's a trojan floating around causing this issue but thought I'd poll the community to see if anyone else ran into this issue or knew the cause?