they can be deleted in the registry.
play with that at your own risk. i'm not going to give you the specific directions because if you're comfortable using the registry you should know what directory to look in.
if you don't know what you're doing you could screw something up. i recommend leaving it alone and letting them drop off on their own.
if you're really interested there was a thread about this not too long ago. you might be able to dig that up through a search.