Sorry I can't give a definitive answer, but my E46 325ti has the same M54 2.5 litre engine and the handbook says 6.5 litres (including filter) so that should at least give you an indication of how much to buy!
Hopefully someone will be along with a definitive answer soon, but at least you have a dipstick to check the level after you've filled it (unlike the facelifts)!