Thunderbolt

Just got an iMac 21.5 inch 2.9ghz.
I have an ssd on my macbook pro that i'm going to use as a boot drive for the imac by using a seagate goflex adapter. I'm also planning to use 250gb of the internal drive as a bootcamp partition for windows 7. Is it possible to use the remaining 750gb to become an "external drive". To explain, be able to boot from the ssd while making the 750gb into usable space for movies and backup data.

Thanks in advance.

Which format should I partition it into?

Yes but i'm using it with a seagate goflex adapter. i'm putting the original hard drive back into the macbook pro and plan to sell it to my friend.