I have two databases that I want to sync with. Can I have both on the same device?

Unfortunately, this is not possible.  Handheld Contact will only sync one device to one Handheld Contact username and one ACT! database.  If you were to set up a second database, and try to sync it to the same device, then Handheld Contact would overwrite the existing data and replace it with the new database.  If you wanted to sync two databases you would need to have two devices as well as two Handheld Contact accounts to sync with.