Just want to clarify for the OP. I cant speak for gamespy, never used it. But Mac Vs Windows civ IV def does work. I've been playing against my windows friends since the mac releases. LAN's work very well and we've been using a VPN to connect to eachother from our respective houses. Just make sure everyone has the same version. I had to have my friends down grade to warlords 2.0 till the mac patch came out. Also, we havent figure out why yet, but I, the only mac user of our group, always has to be the host.