on Zune on the xbox360 some are 720 some 1080 it depends on the movie, but if you have the bandwidth of upwards of 5mbps you can stream HD, and by the way it looks bloody good too.
Ohhhh and if any of you guys are using non cable broadband and you have poor download speed i would suggest getting an "accelerator" from BT, it helps to cut out background noise caused by the cable and helps to increase download speeds