I've been using a program I developed a little while ago to show the speed on a Carputer, thought other people might like to give it a go. You'll need a GPS receiver plugged into Com Port 1 and obviously a carputer of some sort (or laptop).
It shows Speed in MPH & KPH, a 0 to 60 time and a G-Force meter - I have added BHP and power to weight but removed for this release as they are too inaccurate for use.
Download from here... Downloads/Programs section.
Remember I made it for MY use and didn't have anyone else in mind - I could make it more userfriendly if I have enough support though!