I am using the EyeTV Hybrid from ElGato. It will do Composite, Co-ax, and S-Video. It works great for capturing off an old VHS deck through composite. It also works great capturing over the air TV signals if you attach a rabbit ears antenna.
I also have the EyeTV HD which enables capture from Component Video. This is useful for capturing from a cable box in HD.
Both include the EyeTV 3 software, which enables the DVR function.
Here are links.
Several Years ago I tested a program
CaptureMagic SD - Google it
that by using a miniDV Camera also recorded live to my hard disk.
This was able to record in parallel more than one Camera - AS LONG AS - Mac had more than one FireWire PORT (not connectors - but true PORTS - Extra FW-Cards)
I used a PowerBook G4 and one extra FW-port on a "PCM-CIA"-Card and was able to get 2 Cameras running and saving (plus the tapes in them as a safety-belt)
Yours Bengt W