I bought a single copy of HALO. I have a LAN and I installed this copy of HALO on one machine, then the other. When I try to join a LAN game started on the machine downstairs, one the machine upstairs, I get a message that says " You have the wrong CD KEY". I called microcrap and they told me I have to spend another $50.oo and buy a second copy and install it on the machine upstairs in order to play on my own LAN with my son. This is total bullshit. This is the first game ( and I have unreal t 2003, quake3, sold fort 2, motoGP, nascar...etc) that I have ever had to buy two copies of in order to play on my LAN. Insane!!