The game will support LAN and direct IP connections (it just isn't in the beta yet), so you do not need to use Steam at all other than to get the day 1 patch and future updates. You can install the game off the disk, which will reduce the download for the initial patch (though it may be a large patch, with some voiced lines being added). For your second PC you can copy the update from the first (unless you have a Mac/PC combo).
Thanks for the clarification; I have no issues with having it on Steam (I had to get over that a long time ago with many other games) but just wanted to make sure I could play locally if outside access was playing up.
