How do I un-root?

I sold my moment on ebay like a day ago and some s***, the phone currently has 2.1 on it(d003) and the kid that I sold it to want's me to "unroot" it.  To be honest I think he's just a nervous cat who really doen't know too much about this s***... well, its not like I really know what i'm doing either.  Anyway, I suppose to "un-root" this phone I have to bring it back to factory settings, which I assume I would do the same way I did the 2.1 rom in the first place. If that's the case anyone know where I can grab a "factory" 1.5 rom?

Thanks Mang!!  Tried it last night and it worked perfectly.  I had assumed that I would be using the sprint update tool, just the same as I did to get the d003 onto the phone but it never dawned on me that I could use the same s*** that came with it lol.

Anyway, why someone would want a phone with an older, slower, less efficient os on it is beyond me... but I guess some people are just werid like that

cheers

the only option is to use the sprint update tool and flash back to stock....

www.sprint.com/momentupdate (click "details" towards the right side of the screen) that link has all of the information and "tutorial" to follow

what exactly is the problem you are having when using the update tool??