Installing a DD head unit in your car (provided it is the same as all the other e36 cars-which I'm sure it is) is next to impossible.
IF you want a DIN size head unit w/ DVD the Pioneer is an excellent choice. At this point in time, it is one of the best offerings on the market. If you do not require navigation however, the Kenwood KVT-815 is a much more economical decision. I personally like the ergonomics better, and feel the touch screen is more responsive.