http://lolskins.net/
Here is a site that you ll love it.
You can try EVERY skin that you want,but only you can see them.
Is a good way to test the skins before you buy them.
I share it cuz i think that most of you didnt know that site.
How to install it?
1.Create an random folder
2.Put the file into the folder
3.Press the file .exe and you are done.
If doesnt work,as Chyba said,download these 2 files.
http://www.microsoft.com/en-us/download/details.aspx?id=14632 64 bit
http://www.microsoft.com/en-us/download/details.aspx?id=5555 32bit
if one wont work just download the other.