First Read the Read me if they have them but rember some things have changed.
Make a new folder in ...Civilization III\Art\units for each unit you downloaded, unzip the files in to them and rename the folder to the same name as on the INI file, if it has a units_32.pcx cut and paste it in to the end of the units_32.pcx in the ...Civilization III\Art\units folder, if it has "Unit name"Large.pcx and "Unit name"Small.pcx copy them to ..\Civilization III\Art\Civilopeda\Units
In Civ3MultiTool or a hacked Civ3Edit.exe add the unit, change the stats to what you want.