Dell packages OS install disks with most(all?) systems.
If you're talking about home computers, I haven't seen a restore disc included in about 4 years. At most (and even more annoyingly), I've seen them include a friggin'
picture of the restore disc on a little glossy piece of paper, informing you how you can order one.
It's a plain XP/Vista install except it's not subject to activation as long as it's installed on any Dell.
I believe (correct me if I'm wrong, people), that the disc sees a special partition on the drive for verification.