You can develop the report against any database. Here are a couple of options for setting the correct database info:
1. This should work if your application will be installed by a client and that client will have their own connection to a single database. If you're not developing against Oracle (which runs MUCH better using a native connection!) try using an ODBC connection that will have the same name, but point to a different database for each client. If you're hitting Oracle, you can do this same sort of thing with the TNSNames.ora file - have a single alias that will point to a different database for each install.
2. If there will always be multiple databases and you'll only know at runtime which one the report will connect to, you'll have to do this in code. You can find sample code here: Crystal Reports for .NET SDK Samples - Business Intelligence (BusinessObjects) - SCN Wiki - in particular the "Crystal Reports 2008 .NET SDK Tutorial Samples" should have what you're looking for (the code hasn't changed with the newer version of the SDK.)
-Dell