ONE OF THE BEST WAYS:
If you have a Digital8 or MiniDV cam with S-Video Input........take the S-VideoJacK (get a genlock with S-Video) and then input it into the camera and press record.or press Snapshot.
This is the best possible FrameGrabber except maybe WinUAE wich I believe grabs the actual frame.
Do Not use TV capture cards on a PC...........thee is nothing in existence crappier than those to capture true representations. Well except maybe DigiView hehehe.
The way I explained is also great for capturing Better than DVD video OUTPUT from the Amiga. YOu can export it through the FireWire on the camera to make an excellent DVD.
