So if the car cranks but doesnt start up it really shouldnt be that battery.
You have to isolate wether you have lost fuel or spark. (or possible an electrical issue).
Also might be easier to isolate if you have an codes, does your electrical light come up (EML? i think)? Do you have a OBD2 scanner?
1) Open up your gas tank and have a buddy turn the car on, do you hear the Fuel Pump prime (4 second hiss). If not then thats your issue.
2) Unplug your MAF sensor and try start it, failed MAF's have stopped E46s from starting before.
3) How much gas does your tank have? If low, dump a bottle of gas antifreeze and a small jerry of gas and she if it starts.
Another idea would be is to get some car starter spray, or carb cleaner, and spray some into the intake while someone tries to start it. If it revs up some then you know your issue is somewhere in your fuel delivery.