What's the best way to backup and restore Windows XP registry without using any third-party software?

I also don't have my Windows CD handy and I can't access the Backup utility.

ntbackup is a good one you can use it it comes with windows any verson just type ntbackup in the start->run or in a dos prompt like c:\> start ntbackup

if you open the first time then just uncheck the wizard and cancel it.

and try open it for the second time this time it will open and you can see your computer in that you can see the "System state" this is the registry just back it up only this will do next time you can restore it back

it will do good for you.