If you look under the post 'Device Driver when connecting to the PC' (about 16 or 17 posts before this one), I have put some step by step instructions up on how to connect your tablet to your pc. Once you've got the two connected, its just a case of copying your video files from your computer to the tablet. Hope this helps
If the hard drive is mains powered, then it should work fine. If USB powered (i.e. USB connection only) you may get it to work if you plug the tablet into the mains. I certainly have managed to transfer stuff to and from my USB powered hard disk this way.
The trouble here is that you want to view video directly from the drive. If your mains lead is as short as mine, this may be a challenge. Best bet is to invest in a decent 32GB memory card (you can find branded class10 ones for around £20) and transfer the files to that, then view.