UPDATE TO 1.69!
The "Mounted Combat" feat will not work in the upcoming build like the default NWN description states. The following description is tentative.
In order to avoid using a server heartbeat script to loop through every PC that's mounted ever 6 seconds, we will instead be restricting equipment use on horses in the following manner:
*Don't EVER ask for helm model #34 in a reskin, and it will never be at Vanity Plates. Slayings will be free for those who do.