Help Installing Warcraft 3

hi, my friend wants me to install warcraft three on his computer but i have no idea how to do this. i mean, he came to me because i guess i pretty good with computers but i have never heard of this game before. i seen the commercials on tv but never have actually played it. i've seen the trailers of warcraft 1 and 2. i was watching g4tv last night and they showed the new game. so thats all i know about it. so can someone if they know plase give me instruction for the installation of warcraft three. i would really appreciated it.