You need an input/output device. It connects to your MacPro with a PCI card or Firewire cable. Your monitor connects to that box to view the output. Likewise you feed video into the box for capture. You'll have to decide how much you want to spend and how capable the box must be in terms of SD and/or HD. There are many choices.
Blackmagic/DeckLink products
http://www.blackmagic-design.com/products/
Matrox
http://www.matrox.com/video/en/products/mxo2_mini/
AJA
http://www.aja.com/products/kona/
John
MacPro 8-core 2.8GHz 8 GB RAM OS 10.5.5 QT7.5.5 Kona 3 Dual Cinema 23 ATI Radeon HD 3870, 24" TV-Logic Monitor, ATTO ExpressSAS R380 RAID Adapter, PDE enclosure with 8-drive 6TB RAID 5
FCS 2 (FCP 6.0.5, Comp 3.0.5, DVDSP 4.2.1, Color 1.0.3)
Pro Tools HD w SYNC IO, Yamaha DM1000, Millennia Media HV-3C, Neumann U87, Schoeps Mk41 mics, Genelec Monitors, PrimaLT ISDN
