I'm not a FCP or mac user so please bear with me if I'm going to ask a stupid question. Can you output/preview to an external HD monitor? If so is this done directly from the video card within the mac or does one need to buy an additional card / hardware such as AJA or Black Magic?

If you have the appropriate output on your mac hardware, the software is capable of doing it.

Macs don't have an HDSDI out built-in, but many have a second DVI connector which you could hook up to an external monitor or plasma/LCD (through an HDMI adapter, perhaps) and use that as your output monitor.

To get HDSDI, you would need an extra card such as the ones you mentioned. I have no direct experience with those.

Brian,
We are using a dual 3.6 PC with Edius NX PCI express card. Full 1920x1080i
output via analog component. The best playback experience in HD is when using the canopus HQ codec. Using their codec provides 4 to 5 layers of HD
playback in real time on a similar box like we have. Never having to render a chroma key , PIP, crop, or CC for instant playback in full HD rez is a big workflow plus. We have XDCAMHD clips from our F330 and the EX-1 < both MFX file types > and these also load and play back natively but at about 1/2 the realtime power of the canopus codec. Codec quality is excelent and on par with codecs like Cineform. I've seen the NX card on sale for about $1000 including the full EdiusPro 4.5 software. Any hardware option will probably be in the 1-2k price range, but I'm not aware of any that offer this amount of real time playback, < maybe AXio LE but thats quite a bit more $$ >