How to take a decent picture of smoke coming out someone's mouth?

I know to have a black background, and to have a light towards it, but it never comes out right!
I have a nikon D40, and even though the flash doesn't work it still doesn't work with evening lighting. It's so annoying!
do you think if I get the flash fixed, it would work?
what do you do to get a good picture likethat?

You will have to slightly back light the smoke and slightly fill the models face

This will require you to use two light sources. The ratio should be about 2:1 or 3:1, back light to fill

You should use a camera with a flash to capture smoke in the dark.

But you don't have one. So, shine a flashlight through the smoke and directly on the subjects face. It will look cool and be easy.

You need to back or sidelight the smoke with a fairly hard concentrated light source. Don't bother using the onboard flash on the D40 as all it will do is front light the smoke.

Buy a cheap manual flash (YN460-II, £40) and some radio triggers (RF602's, £27) and trigger the flash off camera - this way you can position it where you need it & fire it wirelesly.

You are lucky with the D40 - it can sync with flash at any shutter speed, so you can get rid of ambient light (effectively turn the b/g black) by using a highish shutter speed (1/500 sec).