The disk version / original download version of the game can be be run in Vista/7, though should be run in win9x compatibility mode to avoid a rare bug that can corrupt equipment. There is a workaround for the performance problem, if encountered.
There were Vista/7 compatibility fixes in the most recent update to BD (in the anthology, GOG update, etc), as well as support added for higher resolutions and widescreen aspect ratios. I think the performance problem with more than 3GB RAM should be fixed; I had no problems with a 64 bit Win7 system with 6GB RAM, anyway.
So far there have been two reports of poor performance in BD. One was due to an anti-virus program, and the other reported by someone who gave no further feedback and AFAIK never checked if the amount of RAM Windows could see had any impact on the performance, and just assumed that was the case.
