So that's it. As you remember, developers from id informed us, that DOOM III won't run if you are using Windows 98 / Windows ME. And here is a very simple solution, just install this patch:

• DOOM III AnyOS Patch [1.9 Mb]
  To install this feature take the first disk of the game, replace the default .exe file and then write what you've got on a new CD.

Also there are some mini-modes for DOOM III:

• Fightclub (6 Kb): no weapons, except Fists/Flashlight, headhit does 4 times more damage, run speed has been decreased (now it is like walking), walk speed has been decreased too, now it is two times slower than it was.
• Chainsaws Only (3 Kb): it is simple - you have only chansaw and doubled speed of running, have a nice day! 
• RocketDM (3 Kb): Rocket Launcher is the only weapon of yours! Run speed has been increased by 30% and walk speed has been incesed too by 30%, self damage has been decreased so now you can easily do rocketjump from platform to platform 
• Cooperative (2 Kb): Always wanted to do Doom 3 with a friend? Now you have a chance! This mini-mode allows you to go through single campaign in cooperative mode... like one is using flashlight, the other is trying to hit monster =) 
• 32 players (32 Kb): Fun meat! Now it is posible! Never tried to play on a server with 32 players in? Then do it! This mode breaks the 4 players limit im multiplayer.