Phaelax has answered your question.
To elaborate, lets assume you are using a *.bmp image with a yellow star shape surrounded by black. One way of making the black transparent is using the set image colorkey command followed by the set object command.
If you are using a *.png image then the set image colorkey method doesn't work. Here you need to make sure the black part of the image is transparent by using, say, Paint Shop Pro. Then what you do is just call the set object command.
Philip
What do you mean, bears aren't supposed to wear hats and a tie? P3.2ghz / 1 gig / GeForce FX 5900 128meg / WinXP home