What really helps is to have clean crisp edges on the part of the photo you want to extract. I use the lasso tool and eraser in combination with a mask sometimes. You can also try the Magic Extractor which is part of the Image tool menu. Try and crop as close to the part you want, and then try that. It sometimes does a great job if the areas are well defined.
I am using PSE 4 and think the tools are better in PSE 6. I'm waiting for PSE 7 to be released and then am upgrading to that.