How to use PNG icons?how to make an icon to windows drives?

hi guys, just wanted to ask about how to use png icons in windows folders, as i searched the forum for icons and found them in PNG format, why not in .ico format???
my second question is, how to change the icon of a drive in my computer??
Thanks, and hope anyone can help me.
Answer #1
to change the drive its best to download tuneup utilities 8, it has a styler that helps you change multiple icons at once, but has to be ico format, use the site above =]