I can not find which room has the vent's where you blow up the gas leak i been threw the vault over and over again and i can not find it.

its at the end of a hall right next to the computer you download the data from on the fourth level. just stand in the doorway to the computer room, you can lob a grenade into the vent area (end of the hall) and then quickly shut the door to survive.

PS. if you look at the cieling near the end of the hall you can see the gas.

Also, I cant find Keely. What level is she on?

And is she the one who tells you the "blow up the gas" quest? (I havent encountered it, though I have already downloaded the data)

Thanks

if you havent found keely at all.. then she's down at the far end of a cave (not the one you need the keycard to get into) .. bring up your local map and look at the arrow waaaayyy off outta the vault rooms.. there she is..