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I have no idea but you sound so desperate.

Was there an option to indicate that the rental was to be put onto your iPod?
Can't you just drag it onto it?
Is there a sync option?
What about the transfer purchases feature? (Which I've already forgotten how to do)

I'm sorry, I've never rented a movie that way before.
 
http://support.apple.com/kb/HT1390

Note that if you started playback of the file, you've started a 24 hr countdown before it autodeletes off the computer or the iPod. If you haven't started playback you got 30 days. And if you were impatient and started playback WHILE it was downloading, your 24 hr timer started then...
 
Hook up your iPod and go to the movies tab. If you have any rented movies that are fully downloaded you should see them. Just hit transfer and they get put on your iPod.
 
I've rented a movie using my MBP15, transferred it to my iPod touch, then back again to the MBP15. This was all before I started to watch it.

If memory serves, there is an area under the Movie tab were you can move it.

I don't believe that you can move the movie once you've started watching it.

Edit-1: Downloading a rental movie right now. After DL, I will try and report back.

Edit-2: After you DL the rental movie, connect your iPod touch. Then go to the Movie tab. At the top of the page will be the rental movies. Select which one(s) you want to transfer. When you transfer the rental movie, the rental movie is actually copied/moved. After you transfer, you can transfer back if you want as long as you haven't started playing the movie.
 
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