Is there a software that shows the Reg files?
 

I mean the registry files of a game. Like a software that can detect which new parts are added in the registry when a game is installed.

I need a software like that coz some of my games installs so damn slow and I want to backup it. What I need to do is install and wait for a long time and after the installation, I will use the .iss complier to compile it and make an installer of the installed game on my hd. Problem with thise method however is that I dont have the registry files. Plz help. The games i need to backup are Guilty Gear XX and 25 to Life.

Yes. They are called "registry trackers" (=> google)

Google for 'Regshot' v1.7.2! It can take a 'before' and 'after' snapshot of the registry and show you the changes!

Regmon will show you any changes to the registry in real time.