Yeah the problem with the "easy" track interfaces are that they cost a decent amount of money. Trakmate is very simple the way they've set it up. Their instructions are so easy I figured it out, and they are serial port based which means you can find an adapter from serial to USB if your computer doesn't have a serial port. But you're looking at well over $100 for the entire setup.
Phidget is another USB based interface that RC and several other RMS
packages support. It's native USB, and you can sort of piece together whatever setup you want. But again, it's going to cost you at least as much as Trakmate.
If you want the ultimate in inexpensive easy setups, go webcam. Odds are you already have a webcam lying around. All you need after that is third party software. I think "Zone Trigger" is the one most people use. You basically configure "hot spots" for each lanes Start/Finish line and you're all done. ZT detection motion in the hot spot and you have it configured to run an application with the correct command line when that happens. The application comes with the RMS
(in RC's case it's called "Webcam.exe"). That's it. There are minor trade-offs but in general this is the absolute easiest solution available. If you don't already own a webcam it might run you $50 for the camera and software...