id have to go home to check, but from memory -
as said above you have to put them in the Blizzard folder in Documents for your user account. also (again from memory), SC2Beta won't actually "see" the maps unless you put them inside one of the other folders in the hierarchy. I think I put my replays inside Recent or something like that (I think I left them in a subfolder so they'd stay sort of organized but maybe I dragged them out, I don't recall). Anyway basically once I had them in one of the preexisting folders I could access them from SC2Beta.
One thing that happens is if the replays are from a diff point release, SC2B will prompt you to restart the game, so it can load up the version of the beta necessary to play back that particular replay. Bit tedious but at least we -can- view old replays.