I am fighting some vampires and it says you go down to levels. Can i get those 2 levels back or are the gone forever? If i can get them back how?

clerics have a spell called restoration, use it.
if you don't have a cleric go to a temple

If you where a amulet of power your are imuun for level drain , but you can let your cleric negatife plain protection cast on your party , you can find the amulet of power in the shadow thief guide by the leader , ( I forgot his name )

There is a lesser Restoration spell that your cleric's can cast. This spell removes the level drain but not the damage.
You can go to a temple which has both lesser and greater restoration, the latter completely heals the character.
You can also buy greater restoration scrolls that you can carry with you. I highly recommend that you buy as many as possible for those times when even though your tanks are negative plane protected and someone is wearing the amulet of power, one of your characters that are not protected may get nailed. That way you wont have to spend the time making a run to the nearest temple if you don't have a cleric.
By the way, the cleric spell lesser restoration while removing level drain also does a little bit more damage in the process. I found this out the hard way when Jaheira was drained and critically injured. Upon casting lesser restoration, level drain was removed, she then uncerimoniously died. So be careful using it if your characters are severely injured.