See the question. I want to see the methods and classes offered by a DLLs library.
There's a dependency tracker tool that comes with the Windows SDK (formerly the Platform SDK), it's got a reasonable GUI for looking inside executables and DLL's.
There are also some command line tools that you can use to see inside of dll's, dumpbin in particular - check the MSDN help in visual studio for more information. You can run these tools from the command prompt in the Visual Studio start menu folder.