Why build it when it's already been built? So, OK, pride may make you want to figure it out. But, in case you don't, here is something Microsoft built to do just what you wanted.

Microsoft .NET Framework Setup.exe Bootstrapper Sample

And FYI, I do believe that you can check the registry in VB.NET. I haven't actually tried it but I do know I read about it in one of my books.

Hope this helps.