You can go to a DOS prompt and type scanreg /? to see a list of available options. But in order to actually RUN any of these commands, you'll have to exit Windows and boot to DOS to use them.

In the old days (of Win95), your registry consisted of two files, system.dat and user.dat, both located in the \Windows directory. That's still true with Windows 98, with one significant change. In Windows 95, you always had one backup copy of the registry named system.da0 and user.da0. These files were generated everytime you booted into Windows. Now, in Windows 98, you have at least four copies of past registries. These are generally named RB000.CAB, RB001.CAB, RB002.CAB and RB003.CAB. These multiple backups are stored in your \Windows\Sysbckup directory, which is hidden by default.

One of the more useful SCANREG commands is Scanreg /restore which can be used to restore your Windows 98 machine in the case of a catastrophic registry failure. Running it from DOS (NOT a DOS box within Windows) will give you the menu shown here, with choices to restore from any one of the four backup copies. Note how these copies were also created with each successful boot, and if that's once per day, you can easily return to any day's working copy.