Eric,
You've mentioned a listing for a card in your local area. Do you know if that card is still available? Do you know if it's the 33 or 66 Mhz card? I'm back in the market.
You're right it's for ingesting and output. I'm really not too familiar with all the technical aspects myself, but I know offers a higher quality compression than what comes standard with final cut. It's an older type of card that is becoming obsolete. I don't think it can be used if you use anything after FCP 4.5. Also, at least the card I found, has a PCI connection. If you have a newer mac, the PCI connection has been upgraded to PCIe. To use the card I believe you need a breakout box. This allows you to use composite and component and s-video to ingest and output. I'm learning myself, but I hope that helps a little at least.