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.
Along with the point many other answers point out - talk to your group whether torture is something they care to have roleplayed in their game or skipped over. 

I don't see much value in getting graphic with torture - for me it's enough to say "you're exhausted, bleeding and beat..." and then go into what usually is more interesting as far as that goes - either taunts or threats to things the character cares about. 

"You think duty is not folding or bending. You think duty is you protecting things. What you don't understand is this: we choose you because now the choice is yours - you tell us what we need to know, or your daughter will be the next one we bring into this room. We know you can take the pain? Will she? I hoped you'd be reasonable. I was just trying to protect your family for you..."

For L5R it's especially fun to have people twist the ideals of bushido in their threats.

Mechanically, what you want to do is make it a choice:

**Paying the Price?**

It's been years since I've played L5R so I don't remember the skill list for these things (or it may have changed with 4E).

Tell the player, "There's going to be 3 Torture rolls against your Willpower/(appropriate skill). Each time they get a success, the difference in totals is going to set you up with a choice:

a) fold and give the info
b) take that many points of Disadvantages, permanently, as chosen by me, the GM.

If they beat you by X amount, you automatically fold. Spend your Void wisely."

Aside from obvious physical/mental disadvantages, consider the fact they may pull out OTHER, unrelated, but still powerful information instead. This could be a social disadvantage as they can now blackmail you on other things, or worse yet, a disadvantage to other characters as the PC has spilled dirt/valuable info on someone else.