I am sorry, yea yea yea, i am the corporate monster and all, but on reading this post, i really really really just totally fail to understand what problem anyone would have in respect of difficulties interfacing a PC to a Disco 2, P38, L322 or even the latest LR CAN bus vehicles.
Has no one here ever heard of the industry standard Elm electronics ELM327 chip. It's been around for a couple of years now and you can buy one for a just few quid. It comes with full documentation and PCB schematics as to how to build a full working interface for it.
http://www.elmelectronics.com/DSheets/ELM327DS.pdf
If you are feeling lazy, there are umpteen companies that sell off the shelf hardware that uses this chip and that re ports it's serial RS232 directly or via wi fi, Bluetooth or USB if you prefer, for very little money indeed.
In fact i think even the Chinese have copied it now
Just Google it.
There are also just as many companies providing free OBDII software for it.
We ourselves used one when we first dabbled with CAN bus, and very good it was too.
The chip can be sent very simple and easy to understand ASCII commands over whatever porting is provided by the hardware you have to make it wake up and perform the commonly required and otherwise difficult proprietary vehicle communications actions using comms standards such as ISO 9141.
That means it is 100% able to interface off the shelf, to all Disco II on board systems, all P38 systems except EAS, of which the details on how to knock up a lead for that is already well documented. It will also directly interface any PC with the EMS and gearbox of any L322. However all other systems on the L322 use a BMW bus called DS2. This is different from ISO 9141 only in respect of the fact that it uses pin 8 as opposed to pin 7 of the OBDII connector, which is of course easily rectified with but a blob of solder. ;-)
Giving away trade secrets now i am.
If you want to send it Ascii commands to use its CAN communication capabilities, you can also use it, as i did to send data over the CAN bus to all Range Rover Sports, Disco 3's and Disco 4's the latest L322's Freelender2's and Puma defenders if you wish.
For many years our company has produced software and hardware for all Land Rover models, and while we do prefer to make our own hardware interfaces, I swear there is nothing we could not have used the ELM327 for instead.