Minimally, you should backup:
C:\window\*.pwl (password files)
C:\Windows\Start Menu (or any custom short cuts)
CD-ROM, etc. drivers
To backup Outlook 2000, see MS Knowledgebase Article Q196492 at
Outlook Express is covered in Q270670 at http://support.microsoft.com/support/kb/articles/Q270/6/70.ASP?LN=EN-US&SD=gn&FR=0&qry=Q270670&rnk=1&src=DHCS_MSPSS_gn_SRCH&SPR=OEX
Record any dial-up, browser, and network configuration info.
I would be sure to have two backups of My Documents and any other critical user data. One of them would probably be done with Microsoft Backup (see http://duxcw.com/digest/Howto/software/windows/winme/backup/index.html). Two backups are essential if you are using a tape drive. The next time you just do one backup, you discover the backup is bad, and you lose a lot work, just remember that old guy with the web site, Larry, told you to take the time to do two of them.
If you are doing a clean install on a new hard disk, the old hard disk is a backup. Data can be moved from the old hard disk to the new one by temporarily disconnecting the CD-ROM and plugging the old drive into the secondary IDE interface, or by jumpering the new drive as a Master with a Slave present, jumpering the old drive as a Slave, and attaching the old drive to the same cable as the new one. However, data will usually be transferred faster if the old drive is attached to the secondary IDE interface. I usually keep the stuff on the old drive for a while in case I forget to copy something that I need to the new one. Again, make another backup. I have dropped hard disk drives and I am nearly perfect.
This does not cover everything for every computer. Do it at your own risk. Larry