1) The /PAE switch is not supported (or needed I guess) on a 64-bit OS.

2) Following the migration guide I was reading for moving the SQL service to new hardware, it was recommended that the target SQL server have the "exact same edition and build number" of the source server. This made sense to me since I was copying everything over including my master db and all the other system databases. I didn't know if it would blow up if you fire up a 64-bit SQL 2005 server and attach it to the master db of a 32-bit SQL 2005 server.