Windows Vista Service Pack 2 also supports Blu-Ray, so one would imagine Windows 7 does as well. Although I don't have one to test or anything, I would bet my money on it yes.
if you read one of my links it does say that that they will open it up for vista
what im surprised is that will do the same for XP!!!!
score for those that still have it...lol
the were offering it on M$ connect but i dont know if there are accepting testers..

but they should actually be able to...
im thinking ( this is my theory) that vista has the framework...(for the drm framework...and please no flamewars about this there have been so many.....)
which lets the content owner have control....(please like i stated its fully documented)
which is all encrypted until it gets to the screen
so i will be able to see that wmp wmc will be able to play bluray..
i just dont know how cyberlink is gonna take it though....
edit:my theory is that there will be a separate download which will install the codecs...
just a theory though
this is based on the antitrust cases which M$ has endured