As long as the height & width are standard double DIN (7" wide X 4" high), the only consideration would be depth....
Does anyone know if the G4 can fit into a bmw e46 using the double din bezel, also i dont know how much room there might for it to slot in.
I do not know much about BMWs.
If your BMW is newer, you will need to check if you can hook it up to the factory amplification without any adapters or if you will need any adapters for your vehicle.
I would recomend picking up a dash kit and a wiring harness for your particular vehicle to make installation easier.
you will need to do some serious vent modification..... www.e46fanatics.com and search for double din install (there are about a billion of them, sift through and find the ones with pics.) This is the reason I went with a PC in the trunk.... much easier.