Can You Do This With External USB Hard Drive Storage

Is it possible when using a external HD for your iTunes content to put the content on it via usb ect instead of syncing as my isp is chocking me with data limits

All the best

Unfortunately all iTunes content will need to be synced to the AppleTV.

Transferring movies from your computer to the AppleTV is done over a local network, and should not have any effect on your ISP bandwidth limit.