- Navigate to the following folder: Steam\SteamApps\common\left 4 dead\left4dead\media
- For restoration purposes, make copies of l4d_background.bik and l4d_crashcourse_bg.bik
- Rename l4d_crashcourse_bg.bik to something else.
- Change the name of l4d_background.bik to l4d_crashcourse_bg.bik.
It's a simple process and if you simply prefer the old main menu, don't hesitate to experiment. Steam has a tendency to be capable of fixing most messups by itself. ;]
Small problem with that. The game now defaults to the new DLC's start menu :P Easy fix though, rename the original to "l4d_crashcourse_bg.bik" instead.
Good catch, I updated my post!