To install, scroll all the way down to the bottom of the license agreement and click "I accept the license agreement" and choose "I am 13 years of age or older". Next, just choose the fastest available network speed or close to what your computer has. Just click next for the other things and then you'll have a complete install of a Steam client from 2004.
Unfortunately it seems to hang up when connected online from what I've tested. You can get to the login/sign-up screen in offline mode but there's not much you can do. Hopefully someone with the knowledge can make this client run offline and use any .gcf files in the SteamApps folder, or better yet, get it to connect to Steam's current login servers.