You can’t use any of the DL cards with the 33MHz PCI bus on a DP 1.8GHz G5. This bus configuration has compatibility issues with several video I/O cards. It’s an Apple problem that probably won’t be fixed because of the new, improved PCI-X specification that will eventually replace PCI. I just found this out with my newly purchased DP 2GHz G5 and a DL SP card. You must use a G5 with PCI-X slots. Read this from the Blackmagic website:
The following configurations should not be used with DeckLink systems.