Help With a WD HD.

Hey guys,

I recently backed up about 300 GB of films to a portable HD that I got for Xmas. When I first started to use it, formatted it to use with Time Machine. Then after I heard about Carbon Copy Cloner, I started to use that instead.

I didn't back up the films with CCC or TM, instead I just dragged and dropped all the films to make it easier to back up with CCC.

However, my question is this:

Why can I not play films from the HD without it lagging and running very very slow?

I saw on the Internet that it's possible without any complications, but why cannot I not play them. Is it something to do with the way I formatted it to use with my Mac/Time Machine?

Any help would be great.

Thanks,

Sam