as a recent switcher, I have questions about icons, and people's thoughts on the best method for changing them, the best sites to find sets and all of that.
to change icons, do apple-i (info) for the icon you want to use and the file/folder/etc you want to use the icon on.
once the info screens are up for both, go the icon info window, click on the mini version of the icon, apple-c (copy). go to the target info window, click on the mini version of the target, apple-v (paste).