Preview

Windows Icon: http://www.mediafire.com/?0fwwrzmilrz
Mac OS X Icon: http://www.mediafire.com/?hhhozz5hh1c
Windows Installation
Download the correct file. Unzip the file. (From here on I am not sure if this is the best method, and am unsure if this is different in other versions than Windows 7, if you have a better method or an alternate one for an older OS, please post it and I will edit this post) Create a shortcut of the application in the same folder. Right click, Properties and click the change icon button at the bottom of the properties window. Search for the .ico file that you just downloaded and select it. You can pin it to the taskbar, but you already have that application in the taskbar, you will need to unpin it and repin the shortcut.
Mac Installation
Download the correct file. Unzip the file. Right click, Get Info on the .rsrc file (or command i) and click the icon that shows up in the top left of the info window, it should highlight a little when you click on it. Copy (command c) the icon and do the same with the icon for the folder/application you want to replace, but this time paste (command v) on the icon. It doesn't change the dock icon, so if the folder/application is in your dock you will have to drag it out and replace it.
Hope you like it!