I do have a Windows 2008 Maschine installed with 64 Bit RDBMS 11.1 and have taken successfully some RMAN backups.
Because I have to build a clone database on a Windows 2003 Maschine with a 32 Bit RDBMS (11.2) installed I would like to know if I could use the backups taken in a 64 bit enviroment.
Normally, you can use 64bit RMAN to restore backups done by 32bit RMAN.
You can also restore 64bit RMAN backups with 32bit RMAN provided the database db_block_size is 16K or less. If only certain tablespaces have been created with a 32K block size, then backups of datafiles of those tablespaces would fail to restore.
I've seen this issue with 10.2 64bit RMAN backups restored on 10.2 32bit.
Note: Obviously, you must run utlirp.sql on your cloned database before you start using it.