Sorry to jump in here, but the biggest difference with the 3G is the charging pins. The old charging adapters used the firewire charging pin, where the 3G doesn't support charging with that pin. It uses the USB charging contact on the plug.

I have the OEM iPod adapter in my X5, Z4 M Roadster AND on the Alpine head unit in my 1991 318is e30 and NONE of them will charge the 3G now

Sux!