|First, you have to see if the hardware drivers are available from emachines for Win98. If not, you cannot.|
Second, you need to make sure that the hard drive is PATA (EIDE) or the BIOS can emulate PATA or Win 98 cannot install or run (SATA drivers were never available for it). If neither, you cannot.
Third, You will need to partition the hard drive before you can install Win 98 because there is a limit to the possible drive size supported by it and FAT32. Win98 install disk can format it though.
You need not only the install disk but a non used activation key.
If you do not have a Win98 SE version, you cannot upgrade and there are no more patches available since '98 has not been supported by MS for quite a while.
Finally, IF you are able to do this, your old scanner is unlikely to work well for much longer as it is past what is usually considered its life span. Probably not worth the trouble.
You have to be a little bit crazy to keep you from going insane.