If you use iPhoto, you can select the photos/albums you want to backup, then go to the Share menu and click Burn. This will create a DVD that iPhoto can read later, and will keep any album/event organization, edits to descriptions, and other data just like a Time Machine backup.

If you want a backup that just has the photos, you can consult this help article if you use iPhoto: http://support.apple.com/kb/ht1257 . This disc will be readable on any computer, not just a Mac.

If you don't use iPhoto, simply put in a new DVD, pick a name, drag files to it, then click burn. This is all done in the Finder. More info about the process is here: http://docs.info.apple.com/article.html?path=Mac/10.6/en/8601.html