Best bet is to scan with SpyBot,
If you still have problems then use 'hijack this'. It will produce a log file from which you want to remove the piece of software that is screwing IE up for you. If you are not sure then dont remove anything as this could kill IE altogether.
As a temporary fix you could download the google toolbar. This is normally quite good at stopping your homepage from being changed.
just out of interest what is your homepage being changed to?