SQL Server 2005 provides a lot of benefits over SQL Server 2000 including within the replication feature set.
You might be relieved to know that, although most of the benefits accrue on the side of a SQL Server 2005 Publisher, you can still set up SQL Server 2005 as a subscriber on a SQL Server 2000 Publisher. Thus, you can begin to merge in the newest release of SQL Server into an existing replication scheme. You can read more about this at http://msdn2.microsoft.com/en-us/library/ms217330.
Although major advantage to SQL Server 2005 over 2000 is that changes to the schema, such as through ALTER TABLE statements, replicate out to all subscribing servers. The cool news in a mixed version environment is that the ALTER TABLE statements will be published to SQL Server 2000 Subscribers from a SQL Server 2005 Publisher.
Let me know what you think.