As of 9/12 there are no Decklink drivers for Vegas 8 available.
Decklink drivers for Vegas 8 will be available "soon", from the Blackmagic site.
SCS is collaborating with BMD dev on this initiative and we'll post some further info here once their new drivers are ready.
Unlike in the past version of Vegas, Vegas 8 will always use the current Decklink drivers on the BMD site, and we expect this to be a positive step for everyone, especially if you use multiple products that connect to Decklink hardware.
I'm more than happy to hear this, I'm thrilled! Using the Intensity to view real-time preview to an HDMI-equipped HD monitor will be great. When that happens, I can delete that evil Adobe Premiere CS3 off my hard drive for good. :)