We've been discussing that in this thread:
Multiple Installs on Steam. Is it possible?. Now, I've got Sh3 and SH5 in Steam, but all of my SH4 versions are disk (other than a downloaded v1.5 Uboat Missions from years ago), so I am not certain of the technique working with SH4. There is also this post:
in the FotRSU thread which has a picture of my Steam screen. There is also a link to the
Steam Support Site's method. There are two methods on that page. The "easy" way is if you have more than one hard drive on your computer, you can create another Steam Library folder through the Steam app. If you only have one hard drive, then you have to use the second method "How do I move my existing Steam Installation?", which can be rather involved and take a while, dependent upon how big your Steam Library is.
