I think your talking about the AV (audio/video) plug most cameras will come with them but not all will receive a signal!
That's the one. Some of them don't receive by default, because they're set to output. On my Canon, it's a toggle. Setting one, it inputs from a bulletcam or VCR, setting 2, it outputs to the TV. Worth looking into. If the camera can record from a VCR or other source, you should be able to use a bulletcam with it.
Here's a link with a bit of information:
http://www.bulletcam.com/requirements.htmand a good list of some compatible cameras. I doubt it's exhaustive, but it should give you a good indication of brands that play nice:
http://www.helmetcamera.com/Camera-Compatibility.html I picked up a card for my computer with software for under $150 that has a set up for fire wire to the DV. An input for analog signal for the AV connection also works for the old VHS and an S-Video slot.
You should be able to get a firewire card for under $50 (cdn) and a lot of the software tools that I use, are free. If you want more info, let me know, I'll dig up the info. (It's been a while, so I'd have to look for the stuff that I use.) Also,.. some cameras, like my Canon, come with enough software that you don't need to buy any.