I observed that in the java applet "Charged particle motion in E/M Field" when there exits both magnetic(y-axis) and electric field (x-axis), and initial velocity has only i (x) component, charge drifts in Z direction. B causes charge to make rotational motion and E causes it to drift, this is what I assume. According to my assumption, charge should drift in the direction of electric field, in x direction. 
What is the reason of moving in Z direction? I would like to learn the nature of the motion. My second question is when we solve equation m a = q ( E + V X B ), we get (for conditons above) qE = m dVx/dt which means acceleration is constant in X axis; is it possible for a drifting motion to have constant acceleration?
Thanks for your help
Hasan Serce