It's really simple, just follow the steps.
1) GET STEAM
Don't have steam yet? No problem. Click the following link:
2) CREATING ACCOUNT
You need to follow the steps they give you, I don't need to explain this.
WARNING: You need half-life cd-key for steam!
No Half-Life is no gunman for you.
3) INSTALLING GUNMAN
Ok, after creating an account and installing your games you wish to have, it's time for Gunman. You need to put your rewolf folder (only rewolf, not gunman) into the Half-Life steam directory.
Example: C:\Valve\Steam\SteamApps\E-mail\Half-Life
Or you can also download the folder if you don't have gunman chronicles in the download sector of this site. (NOT ADDED YET)
Ok, extract it and done...
4) GIVING IT THE GUNMAN LOOKS
This is just a little adjustment to it. It gives you a good starting menu.
You'll have to download a patch for this. It can be found at the following link:
I hope....
Now... Restart steam, and you'll have gunman chronicles in your games menu.
Happy Fragging! Cya in the game!