so, today we fight the dragone...
the thing is, its was not as tough as i thought. it managed to drop the mage to -4 hp, and take 16 from teh fighter.
it deals lot of damage (1d8/1d8/3d6), but it had 9 hd, so it was not that hard. so i decide that before they search for treasure, the gnolls started shooting flaming arrows at the "door" (its not a door, i just cant describe it

) of the cavern.
so the players were traped inside.
ok, so they didnt move or anything, they just wait.
to spice things, (and that may be a problem), i added a hill giant. the gnolls "pay" him with goods to help him. he started to throw rocks (and killed a npc, and knocked the mage AGAIN-after the cleric had healed up), then opened space to the gnolls to attack (the giant was too big for the cavern).
so, to stay in topic, i just whant to thank all the ideas. i made the gnolls something like fierce barbarians, and not coward hyenas from "the lion king".