The first beta of Exchange Server 2010 became available a week ago and so we had a chance to test it with ORF 4.2.
The bad news: they are not compatible. The good news: they will be. Luckily, there are only a few changes in the 2010 Beta release that affect ORF, so once we found these changes and modified ORF 4.3, the initial tests ran successfully.
One reason why ORF 4.2 will not work is Exchange detection. We find local Exchange 2007 installations by checking various registry keys and these were changed in Exchange 2010 (actually, as the keys are versioned, it was expected). For instance, what was under HKLM\SOFTWARE\Microsoft\Exchange\v8.0 in Exchange 2007 is now under HKLM\SOFTWARE\Microsoft\ExchangeServer\v14\.
The other show-stopper is the name change of Exchange management PowerShell assembly – this was called Microsoft.Exchange.Management.PowerShell.Admin in Exchange 2007, now it is called Microsoft.Exchange.Management.PowerShell.E2010. Due to the name change, the ORF installer cannot install/uninstall the ORF Transport Agents or query their status.