VB6 only uses a small runtime. Or you could write your app in C++ in Visual Studio 6 and the runtime is built intop all versions of Windows. But it's a retrograde step, .NET is the way of the future, and sooner or later all machines are going to have to have the .NET Framework installed. You may well find that many of the client machines have it already.

Even if you supply the redistributable with your app, 25MB is nothing these days anyway.