Capture Cards that use Direct Show under Windows and do not encode their output will work.
And thanks to Jim's hard work even some devices with encoded output will work, unfortunately we currently do not have a complete list as it still needs more testing. Devices like the HD PVR's Roxio or Elgato's should work, although I dont recommend them (delay problems and they use usb).
If you check for a capture card, post it here before buying and we can at least take a look and give you feedback.