Windows Vista got a pretty bad rap of being a poor gaming operating system. Probably rightly so as it was a bit of a resource hog. Microsoft hopes to correct this with Windows 7, which really, is a very streamlined version of Vista.
TechRadar has some coverage of the immediate benefits seen for gamers in the beta. According to TechRadar the immediate benefits are better RAM utilization and solid 3D performance and driver support. Out of the box Win 7 uses much less memory and does a better job of managing it. On the 3D front Window Vista's mature drivers are fully compatible with Win 7 which should help your 3D Co-Op Gaming!