Don't try. The system databases shouldn't be moved from one version to another. It's really asking for problems.
Script out whatever it is in the master database that you want (logins, roles, server permissions, linked servers) and then run those scripts against the 2005 server. Same with msdb.
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability