The most common (and easiest) way to do this is to simply make a new DKP System, and label the existing one as deprecated, by renaming it to something like "Pre-Dec7th" or "Pre-Cata", and then putting all the new raids into the new "Cataclysm" loot system.
That way your complete history is kept in-tact (points-wise), while allowing you to make a brand new system starting everyone off fresh.
If you'd prefer, though, I can zero out all the points for you, but I tend to prefer the non-destructive approach so that there's a complete history (for example, my old vanilla WoW raiding guild's loot system is still in-tact, if only for nostalgic reasons).
I'm sure with Cata and the reforming of my guild, we'll be starting a new loot system.