i've only ever replaced the shell in the win.ini file ... and the results are amusing
replaced "explorer.exe" with "c:\program files\winamp\winamp.exe"
when the guy's computer booted up (this was a prank on an annoying roommate in college), all that was visible was winamp, smack in the middle of the screen, on top of the ugly windows green background.
aah those were the days
replacing the shell ain't that hard if the replacement's already written. Novell desktop clients used to do that, at least. in win.ini (or boot.ini, forget which) they'd say
Code:
REM shell="explorer.exe"
shell="<path to novell>"
i'm not sure if iit actually overrode explorer or just slapped a new look on top, but meh. it certainly didnt >look< like win98. didn't behave like it either. til i found that file at least, and changed it back to use explorer for the shell