CMS for Pet Charity Site

I am doing this website for free. I don't mind paying for the setup of the CMS but please keep in mind this is an animal rescue site and it's all non profit. :) That being said, the current site is here: [login to view URL] I am currently working on an entire new design. Look over the content of the site because that will not change. I need an admin area that basically allows the others to upload new pet info and images with no knowledge of HTML. All images need to be lightbox/thickbox once completed. Also need to make sure the SEO is present with the CMS. I will post a screenshot when I have the design finished to the project clarification area. Please nobody else post in that section for now. There's no real time frame on this but it does need to be done accurately so good communication is a must!!! Previous proven CMS/SEO work required.