One of the hardest parts of running a lan is finding the perfect balance between keeping those who own the games happy and keeping those who don't involved.
If only 14 out of 50 people own Quake 4... either 14 people are playing and 36 are not, or you spend 2 hours getting those 36 up and running on "unlicensed" versions.
Either way, there is a big downtime involved.
That said... chosing game that 40 out of 50 have is the smarter way to go. Everyone is involved with little downtime.
That is why choosing games is so difficult at a lan, and going to new games is so hard...
See how long it took us to get BF2 involved?