Not entirely sure what you mean by "inputting it into the data acq", but your best bet for reading speed would be to buy an OBD2 tool, such as those sold by
http://www.obdpros.com/(This is an ELM unit, which is compatable with all programs supporting the ELM327 and most programs supporting the ELM323) , and connecting via serial (or via a program), and as you can see from
http://en.wikipedia.org/wiki/OBD-II_PIDs that list, 010D is the command to send to retrieve vehicle speed.