Yes, of course, you can have as many partitions as you want.

Not sure what you mean by losing sync ?

You could just alias the folders from the new drive into the existing folders and tell iTunes and iPhoto NOT to copy imported files, then just import your old libraries or re-create them.

If you want to conform to OS X by keeping all your music in the "iTunes" folder, all your pictures in the "iPhoto" folder, etc, etc. then you *might* be able to mount your new data partition directly to /Users/<your user name>.

Though I can't say for sure since I haven't bothered to try it, I'm not sure it will let you since it's so anal about what it considers "System" folders, but it's worth a try.

In Windows re-mapping a folder is a couple clicks away, in any "normal" *nix it's only an edit away but.....