I am using Photoshop CS3 on an iMac running Snow Leopard.

This is more than likely a very rudimentary question so please forgive my ignorance in advance.
I have a .tiff of a line art drawing I want to include as part of a graffiti scene I am working on.  Its a simple line art on white background on one layer.  I want to get rid of all white pixels; ie make them transparent to just leave the lines.  This drawing will be used on a concrete post so the post's texture needs to be visible through what were the white pixels. I will then experiment with blending options to get the best result. My question is, is there a quick way of removing these pixels. Quicker I mean than using eraser and painting them out manually, which I have started to do but which I simply cannot believe there is not a better way.  I'm an occasional PS user, so please be gentle with me!