hehe lets see if i remember this, i haven't created cows in a good while now even though i join em
u go back to tristrim and grab wirts leg (lower left of map i guess u can say) and go back to town. Put wirts leg and a tomb of town portal in there and transmute. Enjoy
If it dont work, try a scroll of town portal but i'm sure its a tomb of town portal u need lol
Oh, one thing I forgot to mention about the Cow Level:
You can enter the Cow Level as long as you're in the difficulty. Beating the difficulty is only if you need to create the portal with your character.
One trick I do to avoid getting credit for killing the King is to have a character from a higher difficulty create the game, then playing it with a character who hasnt defeated that difficulty.
For example: My Patriarch creates the portal in NM, my character that just defeated normal enters the portal and plays the level. The character in NM cannot get credit for killing king until he's defeated NM difficulty.