I have a Comcast Motorola DCT 3416i HD-DVR box. It has a Firewire connector which outputs 1080i.
I would like to use the Firewire connector to archive to a PC.
Can anyone tell me what software and/or hardware I need to accomplish this?
Thanks.

First step would be to connect the two together to see if your PC recognizes the STB, if it does then you can track down software to use, if it doesn't, your most likely SOL.

Check the Recorders section for more detail, things like this have been discussed in there before.

There is a whole thread on doing this at the top of the page