Windows 98 allows you to set environment variables in the AUTOEXEC.BAT file. Any environment variables set in this fashion are available in every user session.
Add a line to your AUTOEXEC.BAT file that sets the environment variable to the value you want. Consider the following example:
SET ILIB=/NOBACKUP
Because environment variables specified in your AUTOEXEC.BAT file are in effect for every session you start, this is a good place to specify options that you want to apply each time you invoke ILIB. However, after you make a change to your AUTOEXEC.BAT file, you must reboot your system to have the change take effect.