Civ IV multiplayer compatibility question

I’ve recently rediscovered Civ IV. I bought it when it first came out and played a little. At that time I was still bitter about the grand but ultimately failed experiment that was Civ III. Civ IV is far better, but I couldn’t get into it at first because my Civ II strategies were so ingrained and I couldn’t make the adjustment.

Fast forward to a few days ago. A couple of friends of mine were talking about Civ IV, and we decided to set up a play by email game. So far we’ve only played a few turns; in the meantime, I’ve been playing a couple of single player games on Noble. I won the space race last night, and then started looking up threads here and elsewhere about the expansions.

So here’s my question: My friends and I all have the base game (one of them has the Mac version). If I were to install the Beyond the Sword expansion, would I still be able to play against them without forcing them to install it also?

Civfanatics.com is a magnificent resource for all Civ questions.

Just from my own experience, these ways to play live games have all worked for me (everyone is on PCs):

  • I teach Civ4 (both Basic and Warlords) at School, using a LAN
  • I play Civ4 (Basic, Warlords and BeyondtheSword) at home on my network using IP addresses
  • I play Civ4 (both Basic and Warlords) across the Internet - we all use the same version

Even if you install Beyond the Sword, can’t you still run Warlords when playing others who also use it?