Jeff,
Finally, I plan to use RMAN on Win2k to back up DBs on Solaris. Assuming my goal is to be able to restore back to a Solaris box, will it work to run RMAN on Win2k with target DBs on Solaris?
He is using RMAN backup not physical file backup. Why he can't make a auxillary database to a different OS? It will be RMAN who builds the database in physical level and not directly copying from the physical data files. So will you please explain what is the problem?

Say,
original database in Sun Solaris
Catalog database is in NT
backup using rman

Need to create an auxillary database in IBM AIX => you mean to say this is not possible..? Sorry don't have multiple OS to check the possibility..!!

Thanks