If you're thinking about testing Exchange 2010 RC in your Exchange 2007 environment, go ahead. They do work together. However, there are a couple of things you need to know:
- Your Exchange 2007 servers must have SP2 installed. SP2 was released just a few days ago and without it 2010 won't work with 2007.
- You won't be able to see 2007 servers in 2010's management console. This is as designed and you really shouldn't manage 2007 servers with 2010's tools anyway.
- When you install 2010 (I first tried the client access server) and try to use Get-OwaVirtualDirectories to get information about the servers, you'll probably get an error saying Access Denied. You must add Exchange Trusted Subsystem to the local Administrators group on every 2007 server. After that it'll work just fine.
Oh, and one very nice thing: you can upgrade 2010 RC to RTM! So you can start testing and implementing and when the RTM comes out, just upgrade to it. Very nice!