How do I check the transmission fluid level on my 2003 330ci?
BMW sez "lifetime fluid", where "lifetime" really means "until the darn thing breaks down" and needs to be replaced for muchos dollars. Now, if you must check to satisfy your curiosity/angst/whatever, you need a way to get under the car first. Once there, you'll find two plugs screwed in the tranny: top is fill, bottom is drain. Only way to check for proper level is by carefully unscrewing the fill plug and seeing if oil seeps out. If level is low, be sure to put in exactly the same as the original fill: tranny fluid cocktails are definitely a no-no.
As an aside, this morning I dropped off my Bimmer at the dealer and had to take the supervisor out for a test ride so he could hear what was bugging me about the car. Casually, I asked him about a tranny fluid change at 50K. The man was aghast! "No! The high quality fluid used by BMW lasts forever!!"

When he saw that I wasn't gonna buy that official crap, he tried a different tack: "you have to understand that as the fluid ages, viscosity changes and the computer automatically adjusts for this, so if you change the fluid all of a sudden, you are going to have sssudden breakdown since the computer won't know how to compensate for the fresh fluid. Hence, it is a lifetime fill..." :tsk: **Sigh** Something tells me that I need to be finding some way to get the fluid exchanged for when the time comes....