I know that someone on the internet wrote a set of rules to play mordheim with 40k troops. i used to have those rules but i lost them and forgot where i got them from. does anyone know where i can find those rules? i tried googling already.

There actually is such a game from GW, it's called Necromunda, which is quite similar to Mordheim.

Necromunda allows kinda only humans. At the end of the 40k manual you should find rules to play fun skirmishes.

found what i was looking for: http://www.worldinarms.info/