get a fresh craftbukkit.jar, and install modloaderMP this way.
open Craftbukkit.jar with winrar
Open the ModloaderMP zip that you got from this website
There will be another zip in the modloaderMP zip, open that one
now you will see a "net" folder, copy that directly to your craftbukkit.jar
if it asks you to overwright anything, click "yes"
and it should all work now.