As a network admin, I can say that a product like yours could definitely make my life easier...so good job on the effort so far. Hopefully it is not completely taboo to mention actual sofware names, but here we go. (I don't think you would be competing directly with them since they do not create msi packages.)

I have been programming for some time now and there is a real simple yet very effective program that I have always like: Paquet Builder 2.7. A lot of the programs that I create are simple yet very advanced in the system changes that they make. This software allows a whole lot of options when running a package. It also packages all you files and resources into one .exe file. You might just take a look and see what you could incorporate in you software.

One of my favorites is being able to perform tasks before initialization (like copying file, changing reg entries, etc.), and then after installing, but before cleaning up the package...you can do some more.

hope this helps...Regards.