If your used computer does not have an operating system it may not be able to access the CDROM drive without booting from a Windows boot floppy first. In later machines you can change a BIOS setting to enable the PC to boot directly from a CDROM drive but your PC may not have that option. If not then it will require a boot floppy to start you off.
Download a floppy image of your choice from here:
http://www.bootdisk.com/Once you make the boot floppy insert it in your 'new' PC and boot from it (with CDROM access if it asks), Insert the Windows ME CD in the drive and at the A:> prompt type
E:At the E:> prompt type
CD WINME (I think it's called that)
At the E:\WINME\:> prompt type
SETUPThen follow the prompts to install WinME (even though it's the worst operating system on the face of the Earth)
hth