Hi Steve,
The DeckLink v5.0 drivers should be used with Final Cut Pro HD v5.0. Mac OS X 10.3.9 is not officially supported with the DeckLink 5.0 drivers and we advise using one of the two recommended configurations in the technical note at https://www.blackmagic-design.com/support/detail.asp?techID=68. Unofficially, DeckLink 5.0 drivers may work with Mac OS X 10.3.9 but we discourage the use of this operating system. Some of the new DeckLink features, including Blackmagic FrameLink, are exclusively available to Tiger and this is another good reason to upgrade to Tiger.
Regards,
Luke Maslen
Blackmagic Design