Here's what I would put in it:
2Ghz Dual Processor G5
ATI Radeon 9800
Atto Express PCI UL4S SCSI card
Maxtor Atlas 10K Ultra 320 146Gb drive or Seagate Cheetah 10K Ultra 320 146Gb drive
SCSI cable and terminator.

Decklink Extreme - note that long runs of SDI need reclocking with this card.
Aurora Pipe or Aurora Pipe SDI

Powered USB hub.

Keyspan 4 Port High Speed serial interface.

emagic Unitor 8 MkII

Artistic Licence ArtNet box.

A couple of Kramer XGA DA's.

Depending on what environment that you use your Catalyst, you might want to add some decent scan converters too.

Hugh
Catalyst Test bloke.