When attempting to deploy a .NET app on a machine with a version of the .NET framework installed, how can I determine what version it is?

I'm assuming that if the app I'm deploying was built using VS.NET 2003, that it requires the 1.1 version of the framework, but VS.NET 2002 was using the 1.0 version of the framework, and my app won't run with that framework version installed.

Does it make sense to check for the correct version within my application code (and what class or method provides that information), or will it be *completely* impossible to run the application with an out-of-date framework version?

Thanks.