Provided that your graphics card has 2-monitor support and you have an HD monitor attached to the BM card, there should be no problem.
You will have to use a BM codec/preset which some people are unhappy doing, but I manage to get 4 streams of video with the Mercury Playback Engine (hardware mode).
There may still be an issue with the latest CS5.02 patch.I seem to recall that it affects the slip/trim tools.
I run two dvi monitors and a hd plasma connected via a BM card. The BM card also give a sd output which I use to feed a Sony CRT via SDI and a component output which I use to feed a Tektronix WFM. Because of the hardware hd to sd conversion in the BM card the sd outputs are delayed so the lip-sync is not perfect. I have measured the delay and the Plasma picture is 31ms behind the audio (about 3/4 frame) and the sd output is 68ms behind the audio.
Do you have the Audio driver set to asio or windows audio?
I have no delay whatsoever running audio from the Intensity Pro output to an external power amp and selecting it as the default device.
but how to in HD ?
Ah, there's the rub. Currently, PP needs help to do it correctly in HD, and that help often adds complexity and bugs of it's own. Vendors like Blackmagic and AJA offer add-in hardware.
My belief is that modern graphics cards are more than capable of stepping into this role, that PP needs this capability built-in, thus obviating the need for those vendors' additional expense, headaches and limitations. Please, add your voice below.