None of those games have dedicated server software. RTS games in general use basic P2P networking, one person acts as the host (generally the person who creates the game) and everyone else sends/receives their game data through that host. We may see that change in the near future with Heroes of Newerth showing how dedi servers are a massive step up in connectivity for the RTS genre.
You basically just need to ensure the host has the best PC and sufficient bandwidth. Bandwidth shouldn't be a problem in a 10mb or better network with only 6-10 players. In some games (C&C), other peoples computers (other than the host) slowing down can result in everyone's game slowing down as game tries to keep synched up on everyone's machine.
If your going to play other games, especially FPSs, then a dedi server box in your office could be awesome. Each game normally has the server software released with it or available as a download on the game's website, often for both wndows and *nix systems.
