I noticed CMS's are CSS based. Might this be problematic for people who use older browsers? Are there any non-CSS based CMS?
While it could be a problem, you can get a feel for the browser preferences of your visitors by reviewing your logs. Your site logs should be able to give you an idea of what browsers are being used. In many cases, the majority of users will be using one of the more recent versions of IE or FF. As a test, you can install one of the CMS or visit opensourcecms.com to test-drive a particular CMS. Once doing that, disable CSS in your browser and see what happens. -mnc