Sorry i'm a few days late responding to this thread.
1. The wind blow horizontally, so it only has an affect on a_x, not a_y.
2. You can break forces and accelerations into x and y components. Hence:
a_x = K(v_xw)^2
a_y = K(v_y)^2 g for positive values of v_y, and a_y = K(v_y)^2 g for negative values of v_y.
This assumes that air resistance is proportional to velocity squared, and leads to some pretty complicated mathematics that are best solved using numerical techniques. However, if we can model air resistance as being proportional to velocity, the equations become easier and can be solved with a closed form solution:
a_x = K v_x + Kw
a_y = k v_y g
Or in differential equation form:
$\displaystyle \ddot x + k \dot x + Kw = 0$
$\displaystyle \ddot y + k \dot y +g = 0$
Each of these has a solution of the form $\displaystyle x = Ae^{ct} + Bt + C$.
