First, make sure you have all of the latest releases and then install them one at a time. Doing a restore of your "old" data onto the new device spells problems. If you do not have a lot of contacts, this would also be a great time to re do them. When I change devices, I use to have the Desktop convert them; now though, even with a good size address list, I just redo them. It is amazing what jumps out wanting attention.
Google Maps works fine and yes, DateBook Plus works ok, but DateBook 6 at
http://pimlicosoftware.com/datebk6.htm is the big guy on the block.
You will want to delete the old desktop (not the data files though) and install the new desktop. The uninstalling of the old desktop does not delete data files, though to be on the safe side, I suggest changing the folder name to something different. If you are using Vista, then there is a Vista desktop that works fine.