>>>>Under plain Windows XP, the time to bring the server up and deploy the webapps is about 45 seconds on average. Using Windows Vista (the drivers installed between the two OS's are as comparable as I could get them to me), the exact same process takes
65 seconds on average. That's almost a 50% increase, and the only real variable between the two is that Win XP is a non-transactional filesystem, while Vista is transactional.
You should be careful when performing performance tests of a release product build and one that is beta. Currently the Vista builds have all sorts of debuggging hooks and monitors and symbols which of course would not be the case in the final build.