Ridnour has a few problems, the most glaring of which is that he couldn't guard my grandmother. Frankly, he shouldn't be on the 23 man squad at all.
At the World Championships, the PG will be Arenas. Paul will be the backup and Ridnour will either be the 12th man or not be on the WC team. Remember that the offense is going to run through Bryant and James anyway, so the point guard doesn't need to be a great ball distributor, he just needs to be able to take advantage of the open looks he's going to get. Billups is ideal for such a role: he's a good ball distributor, but he's a deadly outside shooter. Of course, Billups won't be on the WC team, so it's moot. Arenas, then, is the logical choice since he's basically a slightly more shoot-first version of Billups.
Paul will be the backup to Billups in '08 and will be the starter by the '10 World Championships unless his career has a mysterious, X-Files type decline or he joins Jay Williams' motorcycle club.