[Tulac]

I'm not sure If I remember it correctly, but if scenario uses civ2 default graphics and rules(meaning it's not a mod), you can just copy that scenario to the folder where scenarios are kept, and you just load them from the game like those scenarios that already came with Civ2...
If you wat to use a mod then, you have to replace files which you got with the mod(mostly civ2.ini, and some .jpg pictures were unit and city graphics are kept), but be sure to safely backup those files somewhere, or you'll be using that mod rules forever...

Also if you want to make your own maps, you can do it by entering the cheat mode, where you can edit the whole world, you can also tamper with civ2.ini file where you can modify a lot of parameters that affect rules(like unit strength, defence etc.), and in the end for the ultimate modding you can make your own graphics, it's not that hard, but modding in Civ3 is much less complicated...