Heres what I found out:
Release date after the release of vista, but not before summer 2006.
Online-Satellite Scenery (kinda google-earth), possibly with the integration of MS TerraServer
Real Traffic with live schedules
weather has effect on surface (eg slippery runway)
Ground Services
Possibility of linking 2 PCs together as Pilot/Copilot
The system specs for vista are a "modern CPU", 512 MB RAM, 3.5 GB on HD.
The information comes from Martin H