Two things you need to remember:
1. You have to run start-msvc9 in mozilla-build as administrator (if you do not your builds will fail with messages about bad file numbers and such)
2. You have to put the following four lines in your .mozconfig (for now – keep your eye out for a new rev of mozilla-build which should fix – current at 1.2)
That’s it – after bug 419665 is checked in, there should be no other obvious issues unless you forget to run as administrator or check out when the tree is burning.
Happy Vista building.