What kind of sum do I have to count on?

Huhu, I just registered here to ask you a question. Maybe you can answer it to me. In March I will be 18 and of course I’m looking for a car for me. Now I wanted to figure out how much I would have to pay for an insurance (with partial cascade). At the moment I have an Alfa Romeo 156 1.9 JTD in my eye (EZ: 07/2000). I think I will have my car insured for the first time with my mother (SF 30%) as a second car. comes from the end of July 2010. Are there any differences between petrol and diesel? So what do you think, how much do I have to pay? If you need more information, just let me know.