(location of civ III - the place you told the computer to install it)/Conquests/Scenarios

Then you place the games files all in one big folder.  Inside this folder, the files must be sorted into two other folders, one for art (named, aptly enough, "Art") and one for text (named "Text").  Inside these folders, the art must be sorted into units files, pedia icons, advisors, whatever requires new artwork, and the text file must be similarly sorted.  If you're not sure what requires a new folder to hold the selected files, look at the core game files.  The scenario folder must be arrayed like that.

That all sounds horribly complex, but thankfully 99% of the time, you don't actually need to do that step, because the creator of the scenario/mod will have done it for you.  So don't lose heart if that sounds like too much work.

The folder must be named the exact same as the file name that the biq file tells the game to look in, or there will be a crash (the game can't find the animations/text/whatever it's looking for).  To be absolutely certain that you name the file correctly, open civedit, and load the biq file.  Open "scenario properties" (located in the Scenario drop down menu at the top) and look where it says "scenario search folders".  This where the game will look for the artwork and stuff.  If it's left blank, the game will use the default animations and text provided in civ3.  Copy whatever is listed here, and paste it as the name of the file with all the custom stuff. 

If you're downloading this scenario from someone else, and other people have played it before, this is often unnecessary, because you can be sure that the folder is already properly named.  In addition, as I said above, the files will already be neatly arranged into their folder, so all you need to do is place it in the scenarios folder.  The reason I gave such detailed instruction is to give you an idea of how it works, and so that you can troubleshoot on your own if you come up with any problems.

Now, open civIII, and click on civ-content.  Select your mod/scenario, and you should be good to go.  If you get a file error, that could mean one of several things.

-You named the folder incorrectly.
-The file specified in the biq file is incorrect.
-The file did not contain all of the information it should have.
-The file became corrupted when you downloaded it (this can happen if it's a large download and/or you have a slower connection).

Some scenarios take a very long time to load the first time you boot them up.  Don't automatically assume your computer is frozen.  One time when starting up a WWII scenario I had to wait close to an hour, while the screen said that it was configuring the scenario.  Just be patient, and maybe bring a book.

If you want to uninstall the mod/scenario, just go back to the scenario file and delete the biq file and game files that contained the custom info.

I should warn you, almost all the scenarios out there now are for civ3 with the Conquests expansion pack, and will not work with vanilla (original, that is) or Play the World expansion pack.  In addition, most require that Conquests is patched up to 1.22.

Good luck and have fun.  And welcome to 1bc.

Thank you!

However, if you actually replaced the default files with the custom ones, then you need to put the default files back in their spot or the game will crash (you DID back up the default files, didn't you?).