How to check if a certain assembly exists?

Question

I'm using the Activator to instantiate a new class based on the short name of an assembly (e.a. 'CustomModule'). It throws a FileNotFoundException, because the assembly isn't there. Is there a way to check if a certain assembly name is present?

I'm using the following code:

System.Runtime.Remoting.ObjectHandle obj = 
    System.Activator.CreateInstance(assemblyName, className);

The main objective is to rather test for the presence of the assembly than to wait for the exception to occur.