Fenixp: As far as I know, there wasn't a secret cow level in Diablo 1, but there WERE 3 cows. And because of them, a ... Diablo-legend started to spread, that there IS a cow level and no one actually knew how to get there. I think Blizzard actually included cow level in D2 because of these rumors
Aliasalpha: I'm pretty sure that D1 DID have a cow level in the Hellfire expansion, I think there was some special town portal scroll that took you there or something
There was still not a Cow Level in Hellfire that I ever heard of, and if there had been a cow level in D1 OR D1:Hellfire, I would have found it, as I compulsively looked for cheats/hacks for my games in those days. (but I never used hacks on battle.net)
However, on the subject of Hellfire, there WAS the CowQuest. In 'vanilla' hellfire, the farmer gave you a rune bomb to 'destroy the hive' .. Wooo! However, there was a .txt file you could add to the hellfire directory, that would open new quests and new classes.
The classes were the Bard (rogue base), the first ever dual-wielder in the Diablo games, interesting, but not all that great. And the Barbarian, who could use 2 handed weapons in one hand, and had NO magic.
The quests:
Theo Quest: a little girl would send you looking for her teddybear.
Cow Quest: No longer is the farmer just a regular old farmer. He's standing there in a cow costume, if you talk to him he'll just go "moo" a lot until you're finally high enough level (and bored enough to keep clicking him), he will tell you that his regular clothes are somewhere in the hive, and he could really use someone to go get them for him.
If you return his clothes, which by the way is a donkey suit, he will give you his cow costume, Bovine Plate extremely powerful full plate armor, that is horrible for dexers and casters. :)
>.> I checked ot see if this had already been posted, but missed it somehow.