There are a couple approaches.
First option - don't. Make real sure your group is on board with this, because many people find scenes like that at the table unacceptable (and it's not just binary, there's also the depth to which you go into it). There's a lot of related topics (loss of control, permanent effects on a character, squeamishness, other psych issues) that really bother people about it.
I and my gaming group aren't really squeamish, so we'd skip past that option, but it's worth saying.
Second option - make it a mechanic. Some games specifically have skills for that - in Alternity, there's both Physical Resolve and Mental Resolve stats that can be used in a simple or complex skill check situation to quickly simulate torture and the PC "giving it up" or successfully holding out/giving false information. In D&D you might use opposed Concentration vs Intimidate/Profession:Torturer, Bluff vs. Sense Motive, or similar. In L5R, there is actually a Low Skill called "Torture," I would assume you'd use that.
The use of Torture is dishonorable
because it involves touching blood,
sweat and dead flesh. When using
Torture, a character is trying to
extract information from the tortured
character using pain. Torture is a
contested Awareness+Torture roll vs.
the opponent's Stamina (deducting a
number of dice equal to his current
Wound level, of course).
The main drawback here is that players always hate control being taken away. Sure, there's always charm and paralyze and stuff, but it is often even more objectionable when there's not the excuse of "it's magic and you failed your save."
Third option - make the PC feel it. Have the torture do not just "hit point" damage - do stat damage, some temporary some permanent (or whatever analogue of that L5R supports - reduce Traits, for example, or apply Disadvantages like "totally jacked up"). See if permanent damage convinces them to talk. The main drawback here is that many players will just opt to die rather than talk, as it's an easy choice to make, and if left with a crippled PC they'll just demand to roll a new character/commit suicide/leave the group and call you names.