High Dynamic Range Imaging

I was really amazed on what Adobe's Photoshop can do. Apart from creating great wallpapers that my friends are obsessed with, I like it from a photographic point of view. I've seen some really great HDR Images around the net. I'm impressed, and I'd like to learn about it.

But my question currently is how many frames does it take to make a good HDR image. I do have a few of my friends who did join a photography club back in my high school days (or Secondary School as some call it) and I'm wondering if any of them know about HDR.

I think I should give it a try and see how it goes.