That config is supported as long as you use SQL2008R2 as your distributor. The relevant rules are in this article:
http://technet.microsoft.com/en-us/library/ms143699.aspx
SQL Server 2008 supports upgrading replicated databases from previous versions of SQL Server; it is not required to stop activity at other nodes while a node is being upgraded. Ensure that you adhere to the rules regarding which versions are supported in a topology:
SQL Server 2000 service pack 3 (SP3) is the minimum version required to participate in a replication topology with SQL Server 2008. There is no minimum version required if you use SQL Server 2005.
A Distributor can be any version as long as it is greater than or equal to the Publisher version (in many cases the Distributor is the same instance as the Publisher).
A Publisher can be any version as long as it less than or equal to the Distributor version.
Subscriber version depends on the type of publication:
A Subscriber to a transactional publication can be any version within two versions of the Publisher version. For example: a SQL Server 2000 Publisher running can have SQL Server 2008 Subscribers; and a SQL Server 2008 Publisher can have SQL Server 2000 Subscribers.
A Subscriber to a merge publication can be any version less than or equal to the Publisher version.
There are no special teachers of virtue, because virtue is taught by the whole community.
--Plato