This is known as a homepage hijacker i encountered one a few months ago after downloading a dodgy codec. Luckily there easily fixable.
I used this tut http://www.pcontech.com/hijacker/rem...com-remove.htm
and the problem was fixed in a less than an hour, follow this tut and you should be fine.
If it works no need to thank.
Need anymore help with this let me know,