Microsoft released…
SQL Server 2005 Compact Edition Developer SDK
…about a month ago. The kit includes a CAB file to install SQL Server 2005 Compact on Pocket PCs and Smartphones running Windows Mobile 2003 and newer.
You can find a Microsoft document about upgrading from SQL Server CE 2.0 to SQL Server 2005 Compact Edition at…
Upgrading from SQL Server CE 2.0 to SQL Server 2005 Compact Edition