Question: How should a GM role-play a torture scene for a PC?

In one of my games, one of my PCs will be captured by the enemy who wishes to get information from him, using... less than ethical methods.

Leaving whether or not the information is divulged to a dice throw seems a waste, but on the other hand, it's hard to force a player to give up info if he doesn't want to.

I'm playing an L5R campaign, with the L5R system.

Answer: 
How I'd do it- less simulation, not too much detail.. but enough that it makes sense in context. The point is, make the scene serve the game. 

For example, I might say as the GM "You get captured..imprisoned for a while, and then one day they torture you. Terrible things happen.. you are permanently scarred (both mentally and physically) by the twisted and painful things that happen to you. However.. what happens is up to you. They keep asking you about (*whatever issue*).. What do you end up telling them?"

Which isn't too graphic, really. And it lets the player decide ultimately what the outcome is. Does he try and bluff? endure? you know.. and also it gives him a hook to roleplay off of (he can decide he hates the race/cause/nation of his torturers, he can decide that he can never allow torture to be used on anyone else.. or maybe he becomes a torturer himself, ala Said in Lost, etc..He develops a phobia of knives.. he loses an ear or an eye or something. The point is- it's all a hook). 

I don't advise going into detail; that's just juvenile, usually. Even if you have the best intentions. 

Hit points are a non-issue, really, although skill checks might make sense. Also talk to the player beforehand about how cool it might be if some info slipped out. Getting a player to pick a losing option on purpose isn't as hard as it seems if you can convince them it makes for a more interesting situation or will in the future.
I suggest the following: make it a part of the narrative. Make the character get hurt. Inflict some damage on him, use insanity rules if your game has them. Get into the character's psyche. Tell the player that if he doesn't comply, he'll get hurt. A lot.