What is "Microsoft Server 2005". If you mean a version of SQL Server 2005,
other than Express version, then yes, you can install Multiple instance of
SQL Server200x in the same computer, regardless its eidtion, be it Express,
Std, or Developer...
It is up to you to make sure the data in the disconnected laptop
update-to-date. since the off-line laptops are only used when the network
server is down, one possible way could be make sure a latest backup of the
SQL Server database is somehow always available somewhere in a mobile media.
Then when its is time to use your off-line app on the laptops, the first
thing the app does is to find the back database file and then restore it to
the SQL Server instance on the laptop. Once the restore is done, your app on
the laptop should have data up-to-date to the point of time of backup.
Just a thought. There could be a lot other ways to do it
Probably you have to, unless you choose other database engine, such as Jet
(MS Access), SQL Server CE...