You would be struggling to get Windows XP up and running on that low-level machine (Duron 900, 128MB memory).
If you want to install another OS, try Windows 2000 Pro instead. As W2K is technically older than ME, you would have to make backups first, then install from scratch. You cannot 'downgrade' over ME.
To get back to your DVD/CD drives:
Go to Start/Settings/Control Panel, double-click System, go to Hardware/Device Manager.
Click on the + before DVD/CD-Rom drives. Rightclick on each entry (one for DVD, one for CD) and select Uninstall.
Reboot the PC. ME should re-install them automatically.