Well, what can I say? If so, congrats, it was an awesome car!
Well the system is no more, so there's not much to put back in! Also you have to understand that this is not like a Pioneer or an Alpine head unit. To make it work, you have to understand what a front end is, what it can do, etc. I suggest you to read around (a lot) to understand what it means to have a carputer. It's basically a hobby, but you'll get that soon.
You're best bet is to install an ipod interface. You can make it work, and display video on the OEM screen, etc., lots of solutions around the net.
If you do, come back to me and I can see what is left from the carputer and I can give you some directions about Infiniti's secrets. The basic is in those pages, if you want me to do it all for you, I might, but I'm going to charge you and arm (but not a leg), okay? :)
woh, what a coincidence, to actually find something like this about a car you bought :)