In the beginning when I started to use window 7, the same problem was also with me, but sooner I found that it is because of automatic window update, whenever an automatic window update occurs you will notice in your programes/file from cpanel that there are some programes (beneficial programes by microsoft) installed on your PC.
So I found it beneficial but as the space on my disk was lower I disabled automatic updates and after then I did not faced any problem like that.

The other solution is that, from your cpanel in your programs, with each update you will find some repeated programs (like you will see a number of versions of C++ and .net, so to keep the space free try to remove the older versions after each updated version is installed.

I hope it will help you.
Thanks.