My Mac Mini has only one firewire 800 port. It is currently dedicated to importing from a Sony HC1.

I'll be adding an external hard drive to be used as a dedicated media drive. If I use a firewire hub the camera and the hard drive will be fighting for the single port when they both need it the most.

Any idea if I'll have better luck with a dedicated USB port for the hard drive, or to share the single firewire port?

Firewire will have a better time handling the distribution of bandwidth. USB is too slow, especially if you have multiple drives all running on USB. USB allocates bandwidth differently than Firewire does, making multiple actions on the same USB bus slower than the same actions on a Firewire bus.

You probably don't need a hub. Just loop the camera through the external drive. I have an iMac which had a Belkin hub until it started to go bad. I took the hub off and haven't had an issue with DV or HDV capture with the decks looped into the FireWire800 drive.

A single firewire connection should have no trouble with two streams like this. You can pass up to 400mbit through firewire (burst) and sustain 350mbit or so. If your video is coming in at (say) 25-50mbit and that is being written to disk then you are well within the limits.