IRC: internet relay chat, it's a protocol for real time chat on the net.
Mirc: one popular IRC interface for windows os. http://www.mirc.com/
One big website of emulation, located in china, far away from us rules. http://www.emuchina.net/
you can download *a lot* of rom from there, but their http server is overbusy most of the time. I suggest you to use the IRC in order to get files from their channel: #emuchina (under the newnet network)
Tosec is a project which make list of *all* roms available on the net, renaming them with the 'tosec standart name' using little utilities. http://tosec.retrogames.com/