I'm just kind of wondering how to convert icons like these. I've tried renaming them to .icns & .png but I get a message that says "Couldn't open the file. It may be corrupt or a file format Preview doesn't recognize" Could anybody help me?

Try Axialis icon workshop, great program for converting, creating or manipulating icons, Mac or PC. There is a demo version, which is what I did before buying. Nice thing is you can save and use your icons you created. Enjoy.

I use a website to download Mac icons that are zipped. When I unzip them, it gives me two folders, one named the icon name which doesn't have anything of value in it. The other is named MacOS or something like that. In that folder is where the Mac icons are. With Axialis all I do is, file open, direct it to that folder and click on one of the icons. If it gives me a perview, it will open and I can convert them to PC. Here is the website I use for Mac icons. Hopefully this will help.
http://interfacelift.com/icons-mac/