I purchased Halo: Anniversary recently and was told by a friend that the maps (which run off the Reach engine) can be downloaded for free for access from within Reach, since I own both Reach and Anniversary. I could not find online how to do this, so is this possible? And if so, how?
When you buy Halo: Combat Evolved Anniversary, you get two components: the original campaign remastered, along with 6 multiplayer maps and 1 Firefight map using the Halo: Reach engine.
If don't own Halo: Reach, you can only play the maps included with Anniversary. There is a Multiplayer option on the title screen of Anniversary that boots up a minimal version of Halo: Reach - namely, only multiplayer with only Anniversary playlists available.
If you bought a new copy of Anniversary, it should have included a code that allows you to download the Anniversary Map Pack for Halo: Reach. Once you have done this, these maps work like any other map pack for Halo: Reach - they are available to play (whether in a custom game or in matchmaking) when you run Halo: Reach.
If you didn't buy Anniversary new (or only want the maps, and not the remastered campaign), the Anniversary Map Pack can be downloaded for 1200MS points.
You can download the anniversary maps for free to use with Reach. A download code is located in the 'Halo: Annivesary' box.