If you can get it, or know a mate who has it, Photoshop Elements (about £50) has an extract tool that is powered by witchcraft - it is unbelievable, and about 100 times easier than doing the same thing in Photoshop. I think they may have incorporated it into Photoshop CS4, but I don't have that so can't confirm.
It's definitely in Photoshop Elements 5 or above.
If you get the chance to give it a go or see it in action try it - you'll be amazed. There might be a demo on Adobe's website.
Mark