How do I "power slide"?
Solution 1:
Apply the brake while in a turn to power slide. That's the right bumper on a 360 controller.
This causes the wheels to lose traction, and the vehicle to move sideways.
Power sliding over an enemy - very difficult.
"Blue Sparks" is a reference to Mario Kart Wii, where power sliding builds up blue sparks. These sparks cause you to boost after the power slide is finished.
Power sliding (aka drifting) in other racing games (such as the Burnout series) allows you to corner more sharply.
Solution 2:
there's a video tutorial that tells you how to do it