Attempt 2
Milandra shut the training cubicle door and locked it. Her brother hurtled into the waiting room beyond, his gold-flecked eyes flaring with temper. “Come out now!” The transparent panel separating them brightened and Milandra configured the grid for a standard training run.
“Father will be furious,” Dannet said. “This was my turn.” He plucked a knife from the weapon’s rack and launched it at the screen. “If you’re so eager to be Chief Warrior, just take his shelking knife.” Desire to earn the Collector by reaching the blade championships rushed the blood through Milandra’s veins in a way Dannet could never understand. The target score of seventy-five blinked from the wall and she responded with an unbidden smile.

Attempt 1
Milandra shut the training cubicle door and locked it. Her brother hurtled into the waiting room beyond, his gold-flecked eyes flaring with temper. “Come out now!” The transparent panel separating them brightened and Milandra configured the grid for a standard training run.
“Father will be furious,” Dannet said. “This was my turn.” He plucked a knife from the weapon’s rack and launched it at the screen. “If it's Father's knife you want, just take it.”
Desire dried Milandra’s throat. Her passion to reach the blade championships raced the blood through her veins in a way Dannet could never understand. Father’s knife, the Collector, was her promised reward for success, and the next step to fulfilling her destiny of succeeding him as Chief Warrior.

[This message has been edited by Twiggy (edited November 06, 2010).]
 

Only one comment - the last two sentences are information dumps. You can get away with the first (easily) but putting the last sentence on, which explains two or three points, is too much. From the build up, you have the perfect opportunity to allow her brother to supply that information through dialog, while at the same time creating further tension between the two.
 

a small nit - when he throws the knife it doesn't make sense to when you just stated she closed herself off - I get that there's and observation room - but loses me at how he is throwing a knife at a screen - I also believe you should stay with the action you can have her think about something but continue her commitment to move forward into whatever is about to erupt.

other than that I would keep reading just to see where it was going.

W.

And, although I don't feel that the last two sentences are blatant infodumps, consider giving us these thoughts and bits of info while Milandra is going through the training run. That, I feel, would be a great continuation of the physical movement you've already established.

S!
S!