Drawing a path for a projectile

For my game (2D platformer), there's a couple weapons that you can throw. I'd like to be able to aim using the mouse and I'm trying to display the path the projectile would follow if you throw it at that angle. I've hit a number of roadblocks, so, here I am. <img src="smileys/smiley5.gif" border="0" align="middle" />

My main problem is the projectiles are influenced by gravity, so it can't be some pre-drawn arc; it has to be dynamic and change as the angle between the player and the mouse changes.

Any ideas on how to approach this?

Isn't it very convienient that near enough the same time you asked mine was released?

Here: http://www.scirra.com/forum/easy-trajectory-w-wind_topic47971.html

Very convenient indeed! <img src="smileys/smiley1.gif" border="0" align="middle" />

One problem, though... I'm probably just missing something, but the trajectories are always only straight lines whenever I click. What am I doing wrong?