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: 
The biggest issue I see with this is whether or not the players will be okay with it. I have learned the hard way that if you're going to be doing any kind of collaborative RPing at *all*, from torture to simple vignettes, you almost *need* to have what story gamers refer to as "the veil":

**If at any time you feel uncomfortable with an idea, a direction, or anything that is happening at a session, you have the right to say "let's draw a veil over that".** At that point, we will stop doing that. The ONLY questions which we can ask are:

* Whether or not it's okay to "fade to black" on a scene and discuss the consequences of it, or if we want to kind of delete the whole thing from the campaign.
* What, exactly, we are drawing the veil over.

And that's all. What you **cannot** ask is "why". The veil is not intended to start a debate but to make everyone comfortable with roleplay. Hopefully it will be used sparingly but it is in my personal experience that some of the worst gaming experiences I and others have had was when someone should have pulled the veil over something but did not (or, in my case, we didn't have the "veil" rule in place and the player did not realize that he had that power).

The veil can cover something as innocuous as a name (perhaps a player's dead wife shared the name of the witch you're using - again, it doesn't matter why) or as extreme as "guys, let's draw the veil over torture".

I realize that you're asking for mechanics here, but I think that ultimately with a topic as contentious as this, this is a more important factor than pure mechanics.
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.