It's important that you follow these instructions, it seems to be the fail-safe way to installing a map.
DRAG & DROP "mud_pit.bsp, mud_pit.res, mud_pit.txt and README.txt in your" Half-Life/tfc/maps folder. DRAG & DROP "mud.wad" in your Half-Life/tfc folder. If you extract the files, most likely winzip will create another folder for the files, and we don't want that. Please just DRAG & DROP the files into the folder.
This level may be distributed via any medium as long as it maintains the name mud_pit.bsp and is supplied in a zip file called mud_pit.zip and contains no other files.
I take no responsiblity for any damage caused by these files. Use at your own risk.