As far as I understand it, to host a feed you need:
1. A scanner/antenna that can pick up the frequencies you want with a headphones or line out jack on the back.
2. A computer with a line in/mic jack on the sound card or motherboard running linux or windows. The computer doesn't need to be very powerful, so it seems like a good use for an older machine that does't get used any more.
3. A permanent connection to the internet (anything more than dial up is fine, dial up is not quite enough)
Basically, you set the scanner to get the freqs you want, then use a cable from the back of your scanner to the computer to feed the scanner output into the computer.
Free software runs on the computer that sends the feed to liveatc.net, where dave reflects it out into the public streams.
You dont even really need a monitor on the machine, once its all set up it just sits there. You could use remote access software like VNC (free) if its a windows box, or ssh if its a linux box to admin the system once its set up.
I'm looking for someone on-airport to house the equipment for me. I will supply all the hardware and set it up and maintain it, they just need to provide me a little space to put the computer/scanner/antenna. I plan on asking dave if I can put the little logo for them in the listing, like you see in a few of the current listings. Makes great sense for an FBO or other on-airport business since lots of pilots visit this site
I think thats the basics of it.