Hi

The W164 aux input should be in the main glovebox, about half way in on the side near the centre console (i.e left side on LHD, right side on RHD)

It is a 3.5mm jack socket, so a normal iPod compatable 3.5mm to 3.5mm lead will work to connected it. You then select AUX input by pressing the AUDIO button twice and then select AUX. I say iPod compatable lead because on some ipod/iphone the jack socket is slightly recessed so some leads won't insert fully.

If you want to install the Mercedes iPod solution, that is very easy on the W164 ML because the head unit comes out very easily. There is a document about this here: -
Mercedes IPOD Retrofit

If you don't want to install it please look in the 'Member Special Offers' forum where you will find some of our Guru's willing to install.

The iPod kit is part number B67824254 and I suggest you get the little iPod tray also to stop iPod rattling around in the glovebox.

You can get the iPod kit from a MB dealer or from here: -
Comand Online Ltd :: iPod Kits :: Mercedes iPod kit for A, B, C, CLK, ML, GL, R Class, Sprinter/Viano/Vito with COMAND or Audio-20-CD
- in the case of comandonline there is normally an offer in the Member Special Offers section of this site for a further discount.