Instead of connecting my camera to my pc I would like to use a device that will convert the firewire signal to composite/component/s-video so I can view my timeline on a TV while editing. Do these devices excist?

I think you're asking two different questions. There are converters that allow a firewire signal to be converted into composite/s-video, and vice versa. Now, to display your NLE's output on a TV, you could use this same device (they usually go both directions.) Your graphics card may already have an s-video output, which will allow you to use the TV as a second monitor, or mirror your regular monitor.

http://www.canopus.com/products/ADVC110/index.php

It didn't look as if any of the Canopus units would accept HDV over the firewire interface. Am I mistaken?

You are correct, the ADVC110 is only for SD. I think only the Blackmagic products convert to and from HD.

Thanks.
I'm using two 21" CRT's on a dualhead VGA card and can select the secondary monitor as an external device in Premiere Pro. This way I can see the video in fullscreen while I'm editing. There's also a S-video output on the card, but it's not that good. If I want to use a TV for proper monitoring I have to hook up my camera by firewire.

ATI made some VGA cards with HDMI output. Can I select a HDTV, connected through HDMI, as a secondary monitor in Premiere or would it be better to go for a special HDMI card (BlackMagic)? Will this work with both SD and HD projects?