228189 Voting system

I run a competition to find the best photograph on a certain subject. I serve my site on a Mac running leopard server, I use wordpress and have gallery2 installed. I want voters to have to register to vote (a winning voter will be given a prize), and they need to review the entries and select the one they like the best, and I need to be able to check on the count as i want, and use the registration database to market to. I need to have logos and banners that can be changed on the site, and some degree of theming/skinning would be great but not essential.