i've tried some solutions found here but no one that do exactly what i want.
Take a look here: http://www.destinationspass.se/dev.asp
The field for uploading an image is by default disabled and radiobuttons above to choose an image is enabled. If a user checks the checkbox i want the upload field to be enabled and the radiobuttons to be unchecked and disabled. When user uncheck the checkbox the field for upload should be disabled and radiobuttons enabled again.