Hello ffaucher,
Simply put for win98, you save the main three components:
[1] system.dat and user.dat in %windir%
[2] each user.dat in user's profile directory individually, if exists
[3] system.ini and win.ini
But, you know you can instruct the system to backup. And also, if default backup copy is not enough, you can increase the number of backup by setting it in system.ini.
regards - tsuji