Windows 2003 Server is the operating system.
Database type refers to which type of database is the report pulling its data from. Is it Oracle, Microsoft SQL Server, IBM DB2, Sybase etcetera. There are dozens of them.
Crystal Reports connects to your database via a particular method. Usually it is ODBC (Open Database Connectivity) but could be one of many other methods.
Whatever method was used to connect to the database when the report was dsigned must also be configured identically on the Crystal Reports Server machine.
If you open the report into Crystal Reports, click on Database, Set Datasource Location and expand out the Properties listing in the Current Data Source Window, you will see the database type.
Whatever it is, this datasource connection must be setup on the Crystal Reports Server box identically to how it is setup on the PC on which Crystal Reports is installed.
When a Crystal Report is published to Crystal Reports Server, it needs the correctly configured datasource to enable the report to run and successfully pull data from your database.