1080P has two versions. One is the ATSC for an HD progressive format that shows 30 frames per second. At this time it is down converted to the scan rate you have your DTV receiver set for. While there are a few displays that have this scan rate it has not been implemented in DTV receivers as an output scan rate nor are there any 1080P sources. A scan rate for the future.
1080P is also a scaler scan rate that is 60 frames per second. Again there are few displays that accept it but they are coming.
For more information go to, Scan rate.