How do you record a movie clip with a .tmp extension to a .xvid format?
Simply renaming the file to something with the intended extension may allow you to play the file in part/full, depending on which parts are missing.
.tmp is a temporary file; it means the file you downloaded never finished downloading completely, and thus the file wont do anything untill it is completely downloaded.
As mkasp said, your file is in incomplete yet. Possibly it wasn't downloaded in full.
As for video actually videos from one video format to another there are many program that can help you with that. See 5 Easy-to-use Freeware Video Converters.