Myth TFL is no longer being maintained by Project Magma, and the last update was more than a decade ago as I write this.
For the best TFL experience on modern computers, we recommend that you play TFL in the Myth II engine with The Fallen Levels plugin. Download it here: http://projectmagma.net/downloads/TFL_Solo/
When you start your campaign, you can enable TFL gameplay if you want the TFL style dwarf bottles and such. Or try it in Myth II mode, which is also fun!
If you want to make the game's interface look more like TFL then download and enable the TFL Interface in Myth2's prefs.
To play TFL multiplayer maps on Myth2, get the TFL Multipack.
For Mac OS X users, be sure to download the Quicktime Cutscenes since the smacker ones cannot be played back on the Mac OS X build.
That all being said - If you want to play the real original TFL, don't let this post stop you from trying. However it is expected that there could be technical problems, and we will not be releasing any fixes or doing any support for this in the future.