If you are transferring from the HD to the Zip Drive, the whole cable will only runa as fast as the slowest drive. You won't technically hrt anything, like Sol said, but transfer speeds will slow some.
Of course, it may not even be enough that you would notice.
By the way, why not just a CD burner? I'm guessing the school has 'em already? I had a chance to grab a ZIP drive at a garage sale, but decided against it because I already got the burner, and that'* cheap and easy.