I just purchsed new movies from iTunes store but to transfer to my ipod, it says it will delete 5 other movies from my other pc. Any ideas?

I have an ipod classic 160gb and it has 145gb available

I have 4 pcs authorized. 1 for each of my family members when I visit. I had recently purchased several movies from the iTunes store before leaving florida, now here in Maryland. I decided to purchsed more. when I attempt to upload from the itunes library to my ipod movies, it gives me a window error explaining:

"This ipod is currently linked to another iTunes library. In order to copy the movie Goonies to this ipod, you must link this ipod with this iTunes library. Doing so will remove 5 movies including Trading Places from this iPod."

Well, this is unaccectable since all my other movies, including the 5 it wishes to remove are on my home PC in florida. All the movies were purchased from iTunes yet only my recent purchases show up in the library folder - which makes no sense unless it auto deletes itself after a period of time?

I have copied the movies from the library folder to this pc just in case but I cannot find a way to copy or backup my ipod to my PC just in case itunes wipes my movies.

Any help or ideas?