Windows 7 install size?

You will have a dead machine in a month. Forget the operating system size. Apart from the OS, wherever you load programs to, windows insists that it's library files are loaded on the system drive. Also all the registry entries associating the libraries with the program. Then there are temporary system files to store. So it fills VERY quickly. Regardless of all the claims, you need AT LEAST 120 GB, and I would totally refuse to install it on less than 250 GB for any customer. I don't want the hassle of trying to save their data when it becomes so loaded it will no longer run.

You need about 5-8 GB for one of the OS's listed below. That's including the apps that come with them, usually movie/audio players, viewers, full office suite, etc. I triple boot on most machines, and usually use 20-40 GB for an OS. Except for Win7, that's a black hole.