Windows 98 Installed over Windows Me?

I built my own computer and had Windows Millenium. BIG mistake and eventually reformated, ditched Me and installed Windows 98.

Customer has Windows Me but with lots of software and files. He needs to keep them but also wants to revert to Windows 98 because of problems from Me.

To my question. “Is it possible to install Windows 98 over Me? Or, because the drive is partitioned could he he format drive C, install Win98, and still be able to access all the software and files he installed andused under Me?