It's a pI3 Windows-only update. Mostly it will provide enhanced movie support -- loading of more than just non-DV AVIs. You'll be able to load WMV, AVI, etc. Possibly MPG and MOV too, but no promises. Also, alpha channels will be supported in movies. (The Mac version of pI3 has all of this already.)
This may end up being 2 updates: one for loading of movies, then one more for writing of movies. Loading of movies works now, but there are some issues I'm working on, mainly speed. It's pretty slow right now. Beta testing of this phase should start in a few weeks.