No worries mate
You should only need the
.pk3 file. Put it into:
C:\Program Files\LucasArts\Star Wars JK II Jedi Outcast\GameData\base
(assuming yours is the auto install-path).
Start a single player game as normal, then bring down the console -
Shift + ` that's the key under your Esc and next to 1.
Then type
map demo and press enter/return.
The demo map will load (no snow though

)
It might be an idea to save the game as soon as the map loads, then you can start the map from the savegame in the future, and not have to do the console thing every time.
Have fun!
