Well you would use one of your unused inputs to hook up to the output from the PLX. I don't know what the unused inputs are on a 2G, I think MAP, BARO(Only if you use lock BARO or a GM MAF), EGR Temp, or the Rear O2, I think those are the available ones. A quick search of the DSMlink forums would yield the answer you are looking for. It doesn't need to be specific for the 250, the 300 would work too, so if you find a thread that says 300 it hooks up the same, just because I have seen a few threads for the 300 on there recently.
Edit:
After looking, this thread has some good info for all the inputs that are available on a 2G:
http://www.dsmlink.com/forums/showth...ight=2G+Inputs