Listen to the advice you've been given so far here, learning to use the tools as well as learning how photoshop actually does what it does are going to be the stongest way of learning. Knocking out backgrounds are one of those things that are very common and also very troublesome at times. Sorry we don't have a specific magic answer for you (that 'magic' wand is misleading isn't it? hehe).

The intention is that you change to a mask and paint away the pixles you don't want to be selected, and paint in the pixels you want to add to the selection. Then come back, post what you found, and perhaps someone who has used PS5 can help you better that I. Also that you take a look in your help file to see whether there is some explanation on what I wrote about. Now I never had PS5, so I suggest you first take a look at your selection menu to see whether there is a 'save selection' command, and also whether on your toolbox you have these two icons shwon in red on the image (quick mask). Infact: both are eachother's opposites: on one hand you have the selected pixels, on the other hand you have the masked ones, which are the ones you do not wish to change. When you save a selection, photoshop saves it as a mask. When you want to paint your door, you will use adeshive tape to protect the areas you don't want to apply paint to. You can change their sensitivity, but you will always have some pixles that *should* be selected, and some that should *not* be selected. You have many tools at your disposal to do this, but none is really perfect. When you 'say' you want to do something with a certain amaount of pixels, people say that these pixels are selected. Now when you want to do something with some pixels, and not with some others, you have to tell photoshop which must be changed and which not. When these pixels are small enough, the brain is fooled into 'seeing' your pic where in fact there are only small coloured dots. That way, the puter can remember the colour of each pixel and its place. Pictures on computers are chopped up into units called pixels so that yopu get a kind of mosaic. What you have to understand is what a selection is, and what a mask. In fact it is very exceptional for the magic wand or lasso tools to do anything perfectly.

Photoshop magic lasso point save