Restoring your IE settings will get rid of the bogus homepage, but it will also reset anything else you have ever changed in the past. And it will only work if this is a 'level-1' hijack (which Yahoo probably is). There are more insidious ways that hackers can bu99er up your IE browser.
Have a read of
this page , there is some freeware called Hijacker Blocker you might want to consider if this is happening frequently to you.