Updated: 6 Aug 2009

http://www.wowinterface.com/downloads/download12965-Carbonite

this should, by default, save on your desktop.

when the download is complete, right click on the newly downloaded file, 

Carbonite-3.210.zip (may not have .zip) 

Choose extract all files, take the default location.  Last dialog box asks if you want to see the extracted files, choose yes.  

In the directory you will see three folders, a license agreement and a readme.

Select the 2 folders, contol click each one.

they should now be highlighted, press control C to copy them.

Now open my computer or whatever vista calls it, so you can see your local C drive.

you locate "program files" then  expand it out, then goto World of Warcraft, then interface, then addons.

Right click on addons, select paste.

Windows will probably say it needs permision, grant it.

should be it....