I have a a 2003 infiniti G35 coupe. It is OBD II. You can connect to it using any ISO compiliant scantool. I use the one from scantool.net. The same should be true for ALL nissans made after 1996.
The things like AutoTap or anything else for nissans, to my knowledge, don't offer anything above and beyond additional manufacturer specific trouble codes for nissans. i.e. they will give you a description for a manufacturer specific trouble code, where others would only give you the trouble code. I heard this is because of the consult scan tool which is proprietary and doesn't work the same as extended OBD II stuff. If you want to get any of the functionality of the consult, I don't think you'll be able to do it using OBD II extended codes. You would have have a consult device or get something that hacked the consult protocol like conZult, but this software is car specific (http://www.ooparts-international.com/id8.htm).
I found a PDF online a while ago that described portions of the consult protocol, I can't seem to find it now, but I have the link in work, I'll try and post it on monday.
I'm currently working on an OBD II plugin format and stevieg (OBDII / Elm MPG meter. Almost working but not quite!) will be making a program to use it that will do a bunch of stuff through standard OBD II. Eventually, if I find the time I will make a plugin that will use the consult interface instead, but I probably won't get around to this until May or so.