Any MCE CD will work with the number printed on the Dell/MS sticker. I've reinstalled the OS on my Dimension 5150 from an Ebuyer CD I bought for another computer. The PC came with MCE preinstalled, together with the mountain of crap and advertising that Dell throw all over it.
Of course, this is no good if you don't have a CD. If you can borrow one then it will work though.
Would I be right in thinking you bought a Dell but didnt get any OS disks with it?
That happened to me so I phoned the CS and explained that I would like to re-install my operating system to suit my own needs and specifications, rather than using the Dell recovery partition. I nicely told them that I found it quire odd that a new PC would ship with no installation disks and that I would like them to send them to me. The CS advisor was very helpful and said they would send the disk out right away. A few days later I got 7 different parcels, each with a disk in it! One of which was the MCE disk. It appears that if you request one disk, you get them all! So now I have duplicates of most (it was only MCe they didnt originally send out with my new PC).
If that's not what you're on about then please ignore me