How are you with editing the registry!
The best way to make sure you've cleared everything pertaining to a program, is to go into the registry type the name of that particular program in the find box..In your case it would be Opera! Then when the find comes across this word Opera just delete it! then press F3, and do the same again until its completed the search through the whole registry. It doesn't take long!
Please backup your registry first though as a
precaution.. Use the export tool in registry to do it..
Using the add & remove in control panel unfortunatly doesn't take everything!