Interorg. Connection Agreement

[didocus]

Hi!
Here is the config:
1. A root W2K domain - "ROOT.NET"

2. A child W2K domain - "CHILD1.ROOT.NET". There is an Exch 5.5 organization and site in this domain - "SITE1" and "ORG1".
A new Exch2000 server is installed in the existing 5.5 site, mailboxes are moved, old Exch 5.5 is deleted. Everything is cool.

QUESTION:
There is another child W2K domain - "CHILD2.ROOT.NET" with another Exch 5.5 organization and site in it - "SITE2" and "ORG2".

What is the best way to upgrade Exch 5.5 in the second domain?
Comparing the different options it seems that most suitable is creating an interorg CA, installing a new Exch2000 in CHILD2 as a server in the existing Exch2000 organization and moving the mailboxes from the old Exch 5.5.

Any suggestions and experience on this matter are welcome!
Thank you!