If both rigs have the same OS, the same installation of GP4 and mods etc. It will work. You will need a crossover cable, not an ethernet cable. Don't try to network it through the router, you are only creating additional problems, a crossover cable is direct pc to pc and was the preferred option, well, the one that actually worked.
Note that you cannot run qualifying. If I recall correctly, the way I got around this was to run hotlaps to determine which driver was quicker, and then used GridTool to modify the grid for the race.
[
www.mediafire.com] Some say you should click it, you know you want to.
[
www.gp4central.com] <----GP4 Central