mitchdog7:
Now, the question that i have is would it be possible to remotely turn on the arduino by touching the screen? Basically, i would wire the arduino to only come on while the ignition is on, but then also come on when i touch the screen - for x seconds. Is this possible? if not, would leaving the arduino on,but turning off the LCD/everything, would this be too hard on the atmega? I don't think that would be too big of a load for my batteries, just wondering if the chip can handle being on constantly. Or could the arduino be put in "sleep" mode.. then woken up on touch?
Most microcontrollers, and specifically the AVR chips used in Arduinos, do have sleep modes. However, this is not something I'd recommend someone new to microcontrollers mess around with during their first project. This is becase using the sleep and wake-up features requires a lower level of control, manipulating bit registers directly rather than using the more intutative commands of the higher level programming (not that this is some dark art or anything, but one should learn to walk before they try to run 
). So I agree with Graynomad, in your case it wouldn't be a problem to have the Arduino powered either all the time or with the ignition controlled electronics.
As far as the chip surviving being on long periods or even constantly, the only potential issue is temperature. The standard Uno uses an ATmega328P, which has a rated operational temperature range of -40°C to +85°C. Assuming the truck has the usual heating and air conditioning capabilities, and if the Arduino is in an enclosure it allows at least a small amount of air flow (e.g. it has a few small ventilation holes), it shouldn't be a problem to keep it well within the rated temperature extremes.
Another thing that will help is paying attention to how you power the board. The on-board voltage regulator can in theory be directly supplied from the truck's battery, and covert it to a steady +5 VDC and +3.3 VDC. However, since it is a linear regulator it does so by turning the the extra power (~7 VDC * upto ~200 mA) into heat. An easy alternative would be to get a USB type power adapter for one of your trucks 12 V outlets and connect it to the Arduino's USB port (which allows both communication and +5 VDC power upto ~500 mA).
mitchdog7:
I realize this project is probably WAY over my head, but I'm up for a challenge.. If it's too much, I'll end up just using this 16x02 lcd display to monitor egt's and a few other engine perimeters i can find/tap into. But i just think a small touchscreen would look SICK.
Using a touch screen graphical LCD shouldn't be too much of a challenge. I would just make sure you get one that has good supporting documentation, along with examples or tutorials about how to intereface it with microcontrollers. It would be especially useful if they had pre-made Arduino libraries. Here's an example of what I mean, there are quite a few other online stores that have similar levels of supporting material. You might find cheaper touch screens from sellers that don't provide any supporting materials, but it will probably cost much more in time and frustration.
It's only the sleep and wake-up modes that I think would be too much for a first-time project.