Hi Roger,
Your assembly name will actually be determined by the project settings (you can look this up or change it in the project properties page in VS). You can also determine in by looking in the \bin directory of the application (for example: Foo.dll would mean the assembly name was "Foo").
I think in the above example I was actually meant namespace instead of assembly name though. This can also be looked up in the project properties page if you are using VB. So if the namespace for the project is "Foo" and your class name is "Bar", you'd change the typename in the ObjectDataSource to "Foo.Bar".
Hope this helps,
Scott