Stalker Shoc is a great game and I personally love to try out all different kinds of Stalker mods, old ones, not so old and the latest.
Some of the mods are designed to work with different updated versions of Stalker, nowadays usually from Patch version 1.4 and 1.5 and 1.6.
I have multiple Installations of Stalker installed on my P.C, from Patch version 1.4 and 1.5 and 1.6.
The way that I have done this is to install Stalker Shadow Of Chernobyl and update it to patch version 1.4, and then I make a folder inside the THQ folder called Stalker Shadow Of Chernobyl 1.4, and then copy the newly patch version of 1.4 into that folder.
Then I update the normal Shadow Of Chernobyl game from patch 1.4 to 1.5, and repeat the process again making a folder called Stalker Shadow Of Chernobyl 1.5 and then copy the newly patched version 1.5 into that folder, and then I do the same for Stalker version 1.6.
I then end up with three patched versions of Stalker Shadow Of Chernobyl 1.4 - 1.5 and 1.6 all inside the THQ folder.
Then inside those folders if it is not already there created I create a folder called mods so that I can save my downloaded mods into the corresponding mods folder.
Another thing I do is make sure I download the files that enable me to not have the Dvd in my drive.
I create a back-up of each Bin folder in each Stalker folder just in case of problems, I then right click on the XR_3DA inside the Bin folder and send a shortcut to my desktop, I then rename that shortcut to the corresponding version of Stalker Shadow Of Chernobyl and in this way I am able to play any version of Stalker I like with any mod that matches the correctly patched version of the game.