I believe the real question Ryan is asking is if can do macro expansion includes (i.e. similar to server side includes in web app development or the way C uses the include <stdio.h> macro. C basically makes a copy of the text in stdio.h and puts it in the place of the line include <stdio.h>. I believe the reason Ryan is probably asking this is to allow him to change the definition of some code and/or resource at runtime. This can't be done this way in .NET. You need to either use Codedom namespace to dynamically generate code, use dynamic binding and a config file (see System.AddDomain for more info) to load dlls at runtime, use config file to store runtime specific info, or use resource files to store locale/environment specific info that can change at runtime. If this is not the reason you were wanting this ability reply with more info about what you're trying to do
FYI - a new feature in the next release of C# is partial classes. This will allow you to split up the definition of a class in multiple files. Check it out it's pretty cool. Whidbey will also be having a realtime refreshed class modeler where updates to the model will be instantly refreshed in the code and vice versa. Pretty cool in deed
As a side note, the splat used in Vipul's first post (System.*) does not work in .NET that's Java. In Java you had to import classes not namespaces (packages) so the splat was used to import all classes in a package. So there isn't really any need for splat in .NET.