According to Tony Hawk's Pro Skater HD developer Robomodo, some of the levels from Tony Hawk's Pro Skater 3 will be released as post-launch DLC. The developer is polling users for which levels to include from THPS3, but Tony Hawk himself will get final say.
Tony Hawk's Pro Skater HD will include levels and gameplay Tony Hawk's Pro Skater 1 and 2, remastered for current gen systems. The game will be released on Xbox Live Arcade and PlayStation Network; it has not yet received a release date, however.