Have anyone install a iPod interface in his/her car and how you do it.
This is my experience

Buy the biggest iPod you can have. "Video 80G", I will explain why later.

Always try to see whether your car have the factory interface available or not. This always the best solution. However, if your car does not have the interface. Try to get a solution using line out not the ear phone.

Cars that I have installed iPod solution below:-

MB E240, Get the ICE-Link interface from Deson and find a good installer to install it into your factory HU. You will lost the CD-Changer. Since ICE-Link don't work with CD-Changer. Once install, Your HU will see the iPod as a CD-Changer and so on.

The reason I said before using a big IPOD is don't put MP3 in the IPOD, Use AIFF format. Its the CD format. The files side is big but its CD Format. You then have a very big CD-Changer.

BMW 330i, BMW have an Aux Input under the arm rest. So don't need to do a lots of work for this setup. Try to buy a charger with line out port and use the best 3.5" interface line and you will get the best music out from the iPod

The ICE-LINK, I brought it on-line and mail over to me from US. Its US$175 for the unit and US$25 for shipping. For MX-5. There are a lots of iPod interface from China that work fine and you can even retain the CD-Changer.

I have no idea about Volvo but if they have factrory interface. It should be the best. However, in Hong Kong. They do charge a lot from the dealer.

AIFF is full CD format. If you only have 4G ipod. It won't take a lots of songs that is why I use the Video 80G. Simple calculation. 1 CD take around 15 to 20 songs and its 640m to 720m so 4GB can properly take 100 songs only, Its around like a 6 CD Changer. My 80G is around 2000 songs