CN=Transport,CN=Rules,CN=Transport Settings,CN=MYNET,CN=Microsoft Exchange,CN=Services
And for Exchange 2010:
CN=TransportVersioned,CN=Rules,CN=Transport Settings,CN=MYNET,CN=Microsoft Exchange,CN=Services
Here's an example.
On my Exchange 2007 server, I created a transport rule to test something for someone that asked a question about blocking spam (the details of the rule are not essential for this discussion).
Note the Exchange 2007 icon in the upper left-hand corner.
This rule was migrated to the Exchange 2010 server:
Note the Exchange 2010 icon in the upper left-hand corner.
Now I create a new rule (TR2) on the Exchange 2007 server...
And a new rule (TR3) on the Exchange 2010 server...
Neither replicate to the other server (which we can observe on the Exchange 2010 server above: the rule TR2 does not appear, only TR3 which was created on the Exchange 2010 server).
At this point, mailbox users that will be migrated to the Exchange 2010 server should be able to send email to both internal and external recipients and also receive email from both internal and external senders.