Sarksbabe! If you still can't do the centaurs part, don't worry! This is what you do :

Start shooting at one of the Centaurs for now, and keep shooting at this Centaur for a little while. If you see the centaurs eyes go green, this means it will turn you to stone!
When the centaur does this, wiggle the directional buttons, or analog stick, etc, about to get free!
After this, start shooting at the one centaur again, until it becomes enraged.
When it does this, do one of those slow motion shoots, and when you shoot it, it will become stunned.
When it is stunned, stop shooting, and throw the grapple at it shield! Now YANK THE SHIELD AWAY FROM THE CENTAUR!
Do this to the other Centaur until both centaurs have lost their shields.
Then start shooting at the one again,
When it's eyes glow green AGAIN, quickly STOP SHOOTING, and IMMEDIATLEY go up to the shields on the floor, and pick one of them up! Hopefully if your fast enough, the centaur will have it's beam deflected BACK-AT IT!
Once one of the centaurs is turned to stone, get a powerful weapon out fast, and shoot at it now! When the centaurs are turned to stone, this is the time when you will do most damage! Hopefully, when you have destroyed one of the centaurs, do the same thign on the other Centaur.

Voila! End of Tihocan's tomb!
Message me abck if you need anymore help!
I've completed the whole game, with all outfits, etc!