Well good question, but one with a simple, 3-letter answer: DOS <gasp!>

You may be able to get into Windows in Safe Mode to do your restoring, so definitely try that FIRST (when you see "Starting Windows 95/98...." during boot, hit the F8 key for Win95, or hold down the CTRL key for Win98, then select Safe Mode.) If Windows won't load in Safe Mode, you can also try using the Command Prompt Only. Now, at this point, if you are simply not comfortable working with files using DOS commands, you will either need to take very good notes with paper and pen, or just leave that Registry alone to begin with. ;)

Since most of you will elect to store your Registry back up files on the same hard drive as Windows, you may as well use the same space already allocated for this purpose. Under Windows 95, a backup of the Registry is automatically created each time you launch Windows and saved under the files names SYSTEM.DA0 and USER.DA0 in the \Windows directory. Windows 98 will automatically create up to 5 backups of the Registry each time you start Windows as well, but those backups are saved in compressed .CAB files in your \Windows\Sysbckup directory instead. Windows 98 will automatically attempt to restore the Registry from the latest backup file if it detects it may be corrupted at startup.

In any way, if you're about to install a risky looking program, new system or multimedia drivers, or about to tweak a few keys in the Registry, you can either overwrite these *.DA0 files, or create all-new files -- maybe SYSTEM1.DA0 and USER1.DA0. Whatever you use for names, write it down!

After you have installed the new software, drivers, or made changes to the Registry, don't wait to be knocked over the head. ;) At the first sign that there may be serious problems (Fatal Exception errors especially), reboot and restore that Registry:

• Click the Start button, and then click Shut Down > Restart In MS-DOS Mode.
  
• From DOS, change to your Windows directory. If your Windows directory is C:\Windows, for instance, you would type:
    cd c:\windows
  
• Type the following DOS commands successively, pressing the Enter key after each line:
    attrib -h -r -s system.*
    copy system.dat system.bak
    copy system.da0 system.dat
    attrib -h -r -s user.*
    copy user.dat user.bak
    copy user.da0 user.dat
    attrib +h +r +s system.*
    attrib +h +r +s user.*
  
• Restart computer.