Dose any one know what type of transmission dose my 1999 BMW 323i have?

I have to replace my transmission. I took it to AAMCO and they seem to have no idea what they are doing. I could use help. I had my car for a week and then the transmission went out. I am looking for the best possible solution. If I replaced the transmission my self would there be any problems that I might run into.

Automatic or manual.

Automatic

There is (2) different types of transmissions in this vehicle. 360R & 325Z....