Update: April 15th, 2008
MediaLab: as above
DirectRT: We are currently on our 6th release of the DirectRT Vista Beta. Let us know if you want to check it out--so far, it's looking good and we are already building improvements into it as we prepare for v2010 which will be both Vista and XP compatible. Do remember though that it remains a beta which means that we make no promises about its performance yet.
Note that the 5th beta is available here (as of April 15th, 2008):
<contact us at service@....com for current beta link>
And the 6th will be available within the next day or so which addresses some installation issues that a couple users have reported. As far as I know there are no functional differences from the 5th beta so long as the install goes ok and no errors are generated when you try to run an input file.