Installing Steam TwiceVideo - Click Here
The reason why its good to have two copies of steam is because you can easily tell which copy is the patched steam and which one is your legit account (if you have one). Keeping cracked steam separate from normal steam is a good idea, unless you want your legit account to be disabled. (Which obviously you don't).
You cannot just run the Steam setup again to install it again, it will not allow you. I will give you the steps on copying and installing steam again.
1. Locate the directory where you installed steam in. Usually this is "C:\Program Files\Steam" or "C:\Valve"
2. Right click steam.exe and press COPY.
3. Make a new folder somewhere SEPARATE from the steam folder (for me, I use C:\Freesteam)
4. Paste steam.exe which you have previously copied into the new directory.
5. Run steam.exe in the NEW DIRECTORY. It should begin downloading all the necessary steam files.