There's nothing wrong with putting up a touch screen for GPS laptop. The only problem is that many GPS software written for laptop do not support touch screen interface - at least not yet, until the GPS industry is becoming more mature .... Unless your touch screen has some sort of driver that can be reprogrammed/remapped to match the touch area with the software display ...
For the receiver, there're plenty out there. I suggest you may want to try the TN-200 USB receiver from Rayming (
www.rayming.com) as I found it to be solid built for in/outside of your car & weather resistant. The one from Delorme can be used ONLY inside your car .... Rayming also has a list of software that can be used with its receiver, anything that supports the NMEA 0183 protocol ... Microsoft Streets & Trips or MapPoint is a good choice for beginner ... You may drive around with it for a while to get the look & feel of driving with a GPS system before eventually you will upgrade to a more sophisticated software that fits your need ...
For power, a 12V-to-110V inverter would be fine. Many laptop power supplies do have voltage regulator to prevent power fluctuation from your car battery ...
Good luck !!!