I didn't know that one actually... Doesn't look like I'll try it soon though.
The Mac instructions on that website may work only in "classic" Mac OS (9.2 and earlier), the TCP/IP control panel has been incorporated into the "Network" panel of System Preferences in Mac OS X (which I'm not giving up for so little;) ), and I couldn't find any reference for a host file, I migh look later more closely, it may be a hidden system file in Mac OS X.
Maybe something similar to the Linux instructions apply as both are Unix based? I'm skittish about playing with the BSD Unix underpinnings of Mac OS X for now.

What I've usually done with obnoxious websites that generate many pop-ups is disable Java Script temporarily, this used to work fine with Netscape browsers, now that I'm using Internet Explorer it doesn't have a separate pref for JavaScript, but I get the chance to close the windows before they load, even if they're in the background.

However I must say that I'm lucky that for some reason in Mac OS browsers Parachat only displays one pop up window at the begining:) , from Antenna conversations I gather that most Windows users get a lot of them.