I'm putting explosions into a game using 3D billboards, and it seems pretty inefficient at the moment, especially when i have about 50-100 of these little explosions on screen at once, since i have to make it calculate stuff, rotate and draw a rectangular mesh every time i want it to display it. And I can't use frames in one big bitmap to animate the explosion. So I'm wondering whether it's possible to do this with D3DXSprite instead. The only problem is working out where on the screen it should be, since I can't tell direct3d to give me the screen co-ords of a certain point in space. So if anyone has a clue how i might do this with sprites please let me know... Thanks

Have you looked at Hardware Point Sprites? I think this is what you need.

How do i pass a flag to the sprite? I can't see any function where i can do that...