For purposes of support, training, demos, etc.
is it possible to run both Billings 2.5 and 3 on the same computer? Anything that needs to be done to do so? Thanks in advance.

It is not possible to run both at the same time.

You can switch between running 2.x and 3.x by renaming the Billings folder in Application Support. Rename only while both apps are not running.

You can't share databases between the two versions (the differences are too vast).

AJ, thanks for the quick reply... sounds like we'll just need yo setup an OS bootable partition to run Billings 2.5 on the same computer.

You can run Bilings 2.5 and 3 in separate user accounts on the same machine.

To go from one to the other I would use Fast User Switching.. see the "Login Options" below the list of users in Accounts in System Preferences.

Great point David, another login is easier than a partition!