Ok, first things first, although an rpm is an rpm, there are distinct differences between the way redhat, suse, and mandrake are setup, so binary rpms for one will not work most of the time for the other two, especially when its a program that relies heavily on the location the distro chooses to put kde in.
This rpm found on rpm.pbone.net should solve your dependency problem.
Once you install that I suggest either you find a kopete rpm that was built specifically for mandrake, or you compile kopete from source.