Well, i have a new post up on this topic with the weapons because i noticed there was more weapons then the silenced pistol and shotgun available when you copy the pak-files. The sounds are messed up (or not working) but besides that its cool to have the new weapons in the game.
Now for your question. Copy all the pak-files from the multiplayer demo /main folder to an empty folder (or one of your choice) and rename them all to be like: multipak0.pak, multipak1.pak and so on.
Next, copy these renamed files to your singleplayer demo /main folder.
In the shortcut to the singleplayer game alter the settings to include these commands
after the link to your exe file:
+set ui_console 1 +set cheats 1 +set thereisnomonkey 1
Then run the game and load up the map. Bring down the console and type
wuss to get all weapons.
Thats about it I think.
