Well, for Diablo 2 it should be pretty easy stuff. You're not worried about complex macros, just broadcasting clicks and a few keys. Are you doing it on multiple PCs? How many game windows? If not, AHK should be able to handle everything without needing any KVM stuff.

The problem I always had with that setup was that the wireless mouse would get out of sync with each other, requiring me to "zero" the mouse frequently (by moving it into the corner of the screen).

Requirements:

* All monitors same resolution.
* All game clients same resolution.
* Non-bluetooth kb/mouse. (so you can pair the same mouse with multiple receivers).