First, we have slipstream effect.  Basically, the air doesn't shoot straight back from the prop; it spirals around the aircraft, and strikes the left side of the vertical stabilizer, which pushes the tail to the right, and thus the nose to the left.

Second, we have torque.  We all know that torque is due to the fact that since the prop is spinning one way, a force is generated that tries to spin the aircraft as well.  Basically, the torque rolls the aircraft left.

P factor is caused by the fact that one side of the propeller produces more thrust than the other.  This is because the Angle of Attack (AoA) of the prop blades is based upon their relative wind.  At rest, it is equal on all blades of the prop (since the relative wind is coming from the rotation of the prop--and nothing else).  With the aircraft flying straight and level, we don't really have this problem, since the wind component caused by the rotation of the prop is the same on all blades, and since the aircraft is level, the airspeed of the aircraft is going to have the same effect on all of the blades equally.  But, if the AIRCRAFT is at a high AOA, one side of the prop circle is ascending, and one is descending.

The problem is, we have airspeed.  So, the descending blade takes a bigger bite of the air than the other blade(s).  Care to guess which one takes the bigger bite?  The one on the right, which yaws the aircraft...LEFT.

The last one (which is a big deal in AH) is gyroscopic precession.  We all know (or should know) that a force exerted on a gyro will come out 90 degrees in the direction of rotation later.  So, what this means for an aircraft is this:  when we push the nose down (when we lift the tail), we are exerting a force on the top of the prop disk, which pushed FORWARD.  OK, 90 degrees later (since the prop spins clockwise viewed from the pilot's seat) we get that force back.  90 degrees later is...on the right.  Which again yaws the aircraft LEFT.

So now that we've got the forces down, how do we take off?  Well, here's a generic procedure:

1. Start engine, use 20 degrees of flaps.
2. Advance engine to 55 InHg MAP (use 45 if you still have problems).
3. Use rudders to track as straight as you can (more on this later).
4. Hold the stick forward.
5. As nose lowers, counter the left yaw--this is a big one too, if you are holding full right rudder while the nose moves, lower the nose slower.
6. As you are level, and at 100 knots, add more power.

Key things to remember-
-Don't add full power right away.
-Don't add full power while you are lowering the nose (this is about the worst thing you can do).
-Track straight--here's an easy way how:  follow your Directional Gyro.  It's possible to take off in a real aircraft with NO visual reference if you have to by sole reference to the directional gyro, and the same is true for Aces High II. 

If the runway heading moves left (at all), press the left rudder.  If it goes right, press the right rudder.  You will notice these changes much faster than if you were looking at the runway trying to perceive the changes in heading.  And, since most of the AH fields are on cardinal headings, and the DG turns the "right" way, this is real easy, and takeoffs are easy to keep on the runway with this method.