I want to change the radio in my BMW 2003 325i, will the 1 din radios fit?

[Dude]

I measured another aftermarket radio/cd player at 7" wide and the BMW radio at 9.5" wide. Can I just buy an installation kit for it or is it too wide. The one I want is a 1 DIN size.
Also, am I looking at alot of hassle/money to get this installed. I hear EVERYTHING is more complicated and expensive for BMWs??