Yes, you can retrieve the movies. You probably need to use the Terminal. Do this:
1. Open iTunes, go to the Music Store, and go to the video that you want to keep. Don't navigate away from the video or iTunes will delete the temp file.
2. In the terminal, enter without quotes: "cd /tmp/501/Temporary\ Items"
Note that the number depends on which user you are on your system (the first one registered, the second one, etc) so you may need to replace 501 with 502, etc.
3. There will be a file named something like QTTemp234234892375. If you don't have tab autocompletion enabled then enter the command "ls" to see all the files. Then do "mv <filename> ~/Desktop" to move it to your desktop.
You can then rename it to whatever you want.