Hi,
Well, beyond the suggestions I've made, I'm not too sure where to go next with this problem. You could try re-installing WinME but you're running the risk of losing the ability to boot to XP if you do.
If it were me, at this point I'd probably be wiping the drive and starting again with the two installations.
Backup anything you want to keep.
Boot with the XP CD to format and partition your drive into at least two partitions.
Stop the installation once formatting has been completed. You're just using the XP CD to do the format and partitioning....
Then install WinME into one partition. Update all drivers etc. Make sure it works.
Finally install WinXP into the other partition. Again update the drivers etc.
Here's a link to a site that will help you configuring for dual boot.
http://www.microsoft.com/windows2000/techinfo/administration/management/mltiboot.asp
(remove spaces from the above URL)
Of course if its not really important to you to have ME, then dont bother. I have dual boot 98SE and XP and I rarely use the 98SE boot.
Cheers,
Tim.