There are windows registry keys involved (and other behind the scenes installation components) for installing the SQL Server Native Client.
For loading the SQL Server Native Client on your workstations for this application, you can find it as a component of the "Feature Pack for Microsoft SQL Server 2005 - April 2006".
Scroll down to the "Microsoft SQL Server Native Client " section and choose the blue highlighted link appropriate for your clients and download the MSI file:
X86 Package (sqlncli.msi) - 3516 KB
X64 Package (sqlncli_x64.msi) - 6403 KB
IA64 Package (sqlncli_ia64.msi) - 8376 KB
Execute the MSI file on each machine. (I am not sure whether or not the user installing the MSI file has to have Administrative rights, but it is safer to be logged in as a local machine Administrator.) Once completed you will need to create a new DSN that uses the SQL Server Native Client driver, that is pointed to the new SQL Server 2005 database. That should be it.
Keep us posted,
MCITP: DBA, MCSE, MCTS: SQL 2005, OCP