When you reinstall OS X from your discs, shut each Mac off with its power button when the "Welcome" screen appears, i.e. before you enter any info.
When their new owners turn the Macs on they will boot to the "Welcome" screen, and they can proceed from there, same as getting a brand new Mac.
Good tip, thank you. I'll be selling an old G5 iMac after reinstall from my OS X discs and was wondering how to get around that issue.
