Were you successful in finding out who the other autograph belongs to? I took a look at the two signatures when you first posted the discussion but I have no idea. My first guess was Peter Sellers but he wasn't alive then. Good luck Chris.
I just did a quick Google Search and Rush was in attendance in 2000 so maybe you can search for the names of other guests in 2000 and start from there.
Interesting, I didn't see the P initially, but it certainly could be a P.
I don't think it belongs to any of the golfers playing that year, but more likely one of the celebrities. I was hoping it was Charles Barkley's but don't think it is his.