Actually, it may not fit just fine. I went through all of this late last year. I have a '00 328Ci. At some point, they changed the antenna input on the back of the stereo. You need to check out the back of the stereo that you are looking at. Make sure it has 2, let me say it again, 2 round jacks somewhere on the back. 1 of them is smaller (the size of a Bic Pen insert) and the other is a bit larger (the size of the outside plastic casing of the pen). Some of the newer radios DO NOT have the larger of the two and if that is the case, everything will work except the radio.
Just so you know...