Are you talking about putting one on or finding ones that others have put on the net? Doing so isn't hard, I've heard of people streaming their audio output, usually as an .ogg feed, or conferencing via chat programs. You can do it for yourself by feeding it into a program such as skype, aim, etc. I did it once by putting my ICOM PCR-1000, a computer controlled receiver with the audio streamed, but took it off after there were too many pissing matches over HF vs. VHF listeners, aero vs. Rail listeners, etc.
Others may be found by going thru the archives of the various rail sites and looking for "scanner feeds". Some even have webcams pointed at various rail junctions, etc. Google may also give you some help as always... Try other folks such as the SWL/UTE Monitoring folks, many of them have their scanners online and may also help
One thing that may impede rail monitoring is that many roads are now using nextel/cell directing to the dispatchers, so many locations may be very quiet now...