I have a problem with the game "Opposing Force" under the Steam
distribution platform.  When I try to play the single-player version
of the game it lags and stutters whenever a new level loads or a new
sound plays for the first time.  This makes the game unplayable.

I had this problem months ago on a different computer.  I went on the
web and found a solution.  It was on a forum (your first clue).  A
person had started a thread and described the same problem that I am
having.  Another person responded with a fix.  I used that fix on my
old computer and it worked great.  But I lost the directions and
cannot find the thread again.

The directions involved a two step process.  The first step involved
dowloading a batch file (I think) that I then ran from the in-game
console.  It preloaded all of the sound files that I would need for
the game.  The second step gave me a list of all of the maps for the
game.  I would then go to the console and type "map mapname" where
mapname was a name of a map.  This preloaded all of the maps.  Some of
the names of maps for the game are: of6a4, of6a4b, of4a1, and so on.

I can get this list of the map names easily enough.  What I am looking
for is a reference to this message thread that I can't seem to find. 
I need a true reference because I need to download that batch file (or
whatever it is) so I can load the sounds.  The forum would probably
have been a Half-Life, CounterStrike, or Opposing Force forum.