Oooh... Laz Posts to the Shrapnel Boards. A rarity nowadays
OK, my thought on this has always been that a modified Elo ranking system would work best. The actual specifc mathematics can be worked out later, but the basic gist is this:
When you join the ladder, you have a ranking of 1000. You gain points when you win, based on the rank of the player you played against. So, if you're at 1000 and beat someone with rank 1200, you gain more points than if you beat someone with rank 800. This is similar to the ranking system the US Chess Federation uses.
This also allows for multiplayer games, through a couple of different algorithms. I'd be willing to help work out the exact algorithms, and also help write up automation for the web.
Eric/LL