It should be a relatively straightforward installation then. The speaker plugs should go straight in to the AVIC connector. You will need to connect the speed signal wire (grey/pink) from the power plug to the speed signal input on the AVIC. Also check that the dash illumination wire (grey/blue) and the antenna feed wire (white) are connected correctly. I didn't connect the reverse or handbrake wires, as I found a small wiring modification to get around the handbrake signal. On the standard installation you cannot watch videos on the move (not that I wanted to do that) or change the navigation destination and settings (which I did want). If you drop me an email, I'll attach the instructions to a reply.
I bought the trim surround from a place on eBay in the US:
http://myworld.ebay.co.uk/euromotorspeed/. It was a bit pricy, but it is a nice fit.
Overall, I'm very happy with mine now. I tweaked a few settings with the aid of
www.avic411.com to change the camera warnings from a stupid barking dog (yes, really), and to get my 'phone book on the unit (my phone wasn't 100% compatible). I also had problems with playing music from SD Cards, but fitting an iPod cured that! It's a much better interface anyway. The navigation is quite good, but sometimes it has trouble keeping up with me at multiple junctions! If a complicated junction is coming up, I tend to glance at the screen beforehand, so that I know which direction I am aiming for.
Edit: If you look at euromotorspeed, don't get one of the full install packages, as there will be loads of stuff you don't need. Just ask them for the surround trim.