You say this is from a flash memory camcorder? Can you be more specific?
Webbie camcorders, like the Flip, may shoot in hi-def, but they also record to a non-standard codec that can cause some of the problems you're describing.
This is aimed a Premiere Pro, but may help
First, work through all of the steps here http://ppro.wikia.com/wiki/Troubleshooting
If your problem isn't fixed after you follow all of the steps, report back with the DETAILS asked for in the questions at the end of that link
The camera in a JVC Everio that does not have HD. It's the same camera I was using on the XP machine.
It turns out this is a MOD file issue. In my XP system I had no problems working directly with the MOD files, but on my Vista machine it does not like the JVC MOD files. I renamed the files to .mpg and they rendered without a problem.