Penetrate Detention Center
As soon as this level begins, instruct all of your teammates to head down towards the grenade position, with one of them actually manning it; you yourself, however, should stay down at the start position. Soon enough, Trandos will begin appearing where you rappelled down and will start to rappell after you; if you hit them with thermals as they line up, you can kill the lot before they hit the ground. Your teammates will take down the rest of the enemies with their blasters.

When you're clear, slice the door near the grenade position. Be sure not to blast it open! Slicing it will merely open the door, revealing the Trando HAM (heavily armored mercenary) within. Your grenadier will start pelting it with sonic grenades, allowing you to finish it off with sniper shots to the head. Be sure your other two teammates are out of sight, as the HAM will probably start shooting at them if it can see them, and it'll make quick work of their health.

Free Imprisoned Wookiees

These slavers are about to get a taste of Wookiee justice...

Now that the HAM is out of the way, you'll have to move through the door to the right of his position and clear out more slavers before you find your first imprisoned wookiee. Obviously, it's going to be locked up nice and tight, so you'll need to slice a terminal in order to free it; as you do so, more Trandos will be coming at you from the doorway beyond the barricade here, so cover the slicer until the Wookiee's free, then set a charge on the wall to bust through. The Wookiee's mad--real mad--and he'll do all the hard work of killing your enemies if you just let him run in. He can die, and probably will in the next room, but for now, just let him go crazy and work out some of that pent-up aggression.

After you walk into the next room, shoot the explosive barrel near the anti-armor position, then walk towards it, but be ready to retreat; a thermal detonator will be chucked at you shortly, and it's best to be elsewhere when it explodes. After it goes off, though, task a soldier to the position, then let the Wookiee get up close and personal with the Trando HAM here. Your anti-armor won't fire while the Wookiee is between it and the HAM, so whip out your sniper rifle and start getting your headshots while it's occupied. The mercs in the corner of the room near the door will continue to chuck out grenades, so you may want to just throw one at them pre-emptively.

Even if the Wookiee survives all this, he'll stay behind at this point, but don't worry; there's another Wookiee in a cell in the next room that you can free. He'll push away the barricade leading outside, so follow him out and kill your way up the tower to the next level.

The Bodyguards

Rescue Tarfful
It appears that Tarfful has been taken from the prison by General Grievous for some reason or another; your job is to get to him and rescue him before he's taken off-planet. Begin by shooting out the spotlight above your spawn point, then start working your way around the corner and killing everyone you see. You have a couple of boxes of thermals in the area, so feel free to use up your current supply as you go through.

After you reach the bacta dispensers, breach the door beyond, then kill everyone in the room there before slicing the terminal. You'll come out to a Wookiee who will sadly depart this mortal coil shortly after kicking all kinds of ass on the Trandos attempting to subdue him--yet another object lesson as to why it's unwise to decorate your pillars with numerous deathly spikes.

Verify Grievous Presence on Kashyyyk

If you want to see more of Grievous, you'll have to wait for the third prequel to hit in May--his appearance in Republic Commando is fairly brief.

After the Wookiee dies off, you'll be commanded to verify that Grievous is indeed planetside. Doing so is a simple matter of walking up to a viewport on the upper level of this room and looking out the window; you'll see Grievous along with one of his dreadguards in the landing pad below. Unfortunately, you'll be spotted, which should lend a sense of urgency to your movements; if you don't get down to Tarfful soon, he'll be taken off planet and you won't be able to rescue him.

To get to him, you'll need to place a charge near the window, then place another on the forcefield lining Tarfful's cage nearby. As this charge is being laid, numerous Trandos will be coming at you from the far end of the corridor, so whip out your sniper rifle and start blasting them.