Original post: http://forums.steampowered.com/forums/showthread.php?t=1756923
All credit goes to MenaceInc for the patch and guide.
This patch utilizes the DarkPlaces engine developed by LordHavoc, the plasmagun fix by OoPpEe, the music patch originally hosted on widescreengamingforum.com
and the NSIS install system developed by Nullsoft.
PLEASE NOTE THAT THIS PATCH IS FOR STEAM VERSIONS ONLY!
This patch can be used with the retail versions of Quake but the default directory is that of the Steam version. If you do install over a retail version, please ensure that there is no separate opengl32.dll in the install folder.
These patches will install music for Quake, Quake Mission Pack 1 and Quake Mission Pack 2.
This will come to a total of ~80MB of space for all of the patches.
I've also included a custom config.cfg for more modern default fps controls.
Please note as well that selecting Delete Local Content on Steam will not delete the music or dll files included.
These will have to be manually deleted.
Also, trying to Verify integrity of game cache will result in the game files being overwritten with the originals.
If you try installing one of the Mission Add-ons, you will need to reinstall this patch as Steam rewrites over the modified files.