How do i restore image file types?

Hi, I have a computer running win98 SE my problem is that i install a third party software to open images. The software works fine, i have no prob with that. What happen was that i decided to uninstall the software by using the uninstall prog that came with it. But now when i try to open any image file, the open with.. box appers asking me that could not open file since picviewer.exe was not found.. I delete the file extension from windows explorer but now i can’t set the default file extensionthat was before i install the software.. i also delete the entries on the REgistry.. Any help would be apreciate

Thanks

Ismael