There is a "System Restore" facility in Windows ME but not in Windows 98. Which do you have as there isn't a "98 ME"?
For 98, you can restore an earlier version of the registry by booting with a Windows 98 Startup Disk (boot floppy) and at the "A:\>" prompt typing:
and pressing Enter. You will then have the option to restore one of several previous copies of the registry. In Win ME, there should be an option from the Start Menu to launch System Restore - possibly "Start > Programs > Accessories > System Tools > System Restore", but I don't have Win ME running at the moment to check the exact location.