Synching your Xbox 360 with your Computer's library

Someone help me out. After saving a replay for Halo 3, how do I send it over to my Computer's library? I just passed the point where it shows me the 8 digit code and now it wants me to go www.xbox.com/pcsetup. All the xbox is telling me is go to that website and upgrade (upgrade what?)... Enter the 8 digit code. However, going to that website they give me a long list of downloads and pretty complicated instructions for each one.

p.s. I already downloaded the new windows media player and I have allowed the computer to share files with the xbox. what else

A response will be much appreciated