[oie]

I'm using my ipod as an external hard drive, if I plug it into another computer, I know that it can automatically sync the music on that itunes to my ipod, but will it clear out the external hard drive as well?

[awdark]

If you don't open iTunes it wont start the sync (if you're cautious disable automatic sync in the itunes options before you plug it in)
But even if it does decide to wipe the music it doesn't erase your data on the data part of the drive.