Multiple Instances SQL2K and 2005

Hi, we have a 2 node cluster running Server 2003 with a single instance of SQL 2005. We are looking to migrate as many apps as possible to SQL 2005, but will likely need to keep a SQL2000 instance. In addition, we want to isolate some of the SQL databases that are web accessible and will setup an instance for that. So, are there any reservations running this:

(2) SQL 2005 instances
(1) SQL 2000 instance

on the same cluster? We have Enterprise edition of the OS and SQL Server. We plan to run a multi instance setup with an active and passive node so all 3 instances would run on the same node. The hardware should be able to handle all 3 instances.

Also, any special steps to install SQL service packs in this scenario?

Thanks,
TJ

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