Yesterday I upgraded an old Gateway 2000 PC from Windows 98 SE to ME.  I
have performed exactly this upgrade to four PC's in the recent past
without any problems.  Not so this time.  I upgraded in order to use a
USB flash drive, which I have been able to use on those four other PC's.  
When I inserted the device, Windows ME put up a window saying that it had
discovered new hardware and would install it.  It trundled for a while.  
Then a window popped up saying that Windows Explorer had encountered a
problem and had to close.  I had to reboot.  When I tried to open
Explorer after the reboot, the same thing happened.  I removed the flash
drive and Explorer worked properly.

I reinstalled ME from the same CD.  The result was the same.

When I first installed ME, I selected the recommended option of
preserving the existing 98 SE setup.  I understood that this would allow
me to revert to the prior operating system.  (????)  Unfortunately, I don't
know
how to do this.

Explorer shows a RESTORE folder.  Properties says the size is 18 MB.  

That doesn't seem large enough to re-establish the OS.  This folder holds
four files:

DISKCFG.DAT    1 kb DAT File
SRDISKID                    1 kb DAT File
VxDMon.cfg    1 KB CFG File
VxDMon.dat    61 KB DAT File

That doesn't add up to 18 MB.  I have hidden files and file extensions
showing.

Disk Cleanup shows: Delete Windows uninstall information  155.73 MB.

This doesn't make much sense to me.

Can I really revert to 98 SE?  If I can, please tell me how to do it.