You certainly can.
You will however need to have a PC or laptop connected to the PS3 to do this. You the run a media server program on the PC, and stream your files from the pc to the PS3. via a cabled network preferably. it's a pretty simple solution.
Nowhere near as simple as the WDTV though.
No, you cannot just hook your external straight to the PS3 and play the files from there. The PS3 just won't recognize most of the file formats.