Ok.......Im not too sure exactly what you know about any parts of the project, so i appologise if i offend you by going through some of the basics. If on the other hand i go over something which you dont quite understand, let me know and i'll try my best to help you out.
Ok first thing is first, Im not totaly clued up on all the details of dodge's diagnostic/obd compatibility. Do you know if your dodge is OBD/ OBDII compliant?
If it is OBD/ OBDII compliant then you shall have an diagnostics socket somewhere within the vehicle. Usualy under the dash, not too sure about dodge (check your manual)
Then for starters you can purchase and hook-up a diagnostic "scantool" such as Elm 327or OBDlink by scantool.net
The scantool plugs into the OBD diagnostics socket on your vehicle and links to a computer. The computer sends commands to the scantool which will read the parapmeters of the enigine e.g. RPM, engine load etc.
This would enable you to complete the In-car computer part of your question where you can read the vehicle parapmeters
As for the PIC, you would have to write an application program for the computer to send commands to the LCD via the PIC. One of the programs i have used for this type of project is visual basic by microsoft (Express version FREE to download from microsoft). It is fairly simple to use.
Once the computer can send commands to the PIC, the PIC has to be able interpret and action these comands as you require (I.E. Send codes to the LCD) You would have to write a program for the PIC.
You will also need to know how to connect all the electronic components together to function correctly. The PIC i have used is the PICAXE from www.rev-ed.co.uk/picaxe/
They provide great datasheets on all the programming commands, Input/output components and how they are conected etc.
I certainly would not say this was a very easy project. It would certainly be achievable but time consuming. There is probably a few things that you would have to learn about to carry out this project.
Let me know what you think about what i have writen (good or bad), if there is any questions let me know and i'll try my best to help you out.