Is this still in place? If so, what's the exact command set? Do I just sneak up behind something and type 'mount mekillot'?
Next, is this a ranger-only thing, and is it dependant on the ride skill? And afterwards, is that creature going to be pissed at me?
I've got a fun idea for a character, if you can't tell :P
I ran acrossed a beetle before, I tried to mount it, I mounted it, I got thrown off, it wasn't happy and a fight pursued.
Hope thats a help.
Creeper
I'm pretty sure it's dependant on your ride skill, and I'm also pretty sure other classes can get their skill that high, but I believe Rangers, Half-Elves, and especially Half-elven Rangers have a much better chance at achieving these levels of ride and mounting.
Note that there are some creatures you can't mount. But that's just IC if you think about it.