What's the purpose of the DVD?
When you use the Share -> Burn command in iPhotot it makes a "mini-iPhoto Library" on the Disk, complete with database, thumbnail and preview files. These are no included on the calculation in the iPhoto Window. This method of burning is designed for sharing with other iPhoto users or as a (limited) back up option.
If you want to just share snaps with other computer users then File -> Export and send them to a folder on the Desktop, Burn that to disk with the Finder.