Hello--I just recently got Photoshop CS3 and I need help with some photos. I'm trying to take one part of one photo and put it into another photo. For example, I'm cropping out a person in one picture---and I want to put her into the other photo, as though she'd been there. I cropped it and tried to place it, but it either brings the whole picture..not just the cropped part. I need help!! Thanks.

The crop tool is for selecting areas in an image, where you would want to discard everything else outside of the crop...

For selecting just the person, you'd want to go around the whole image you want with maybe the Pentool or the lasso *if you're really steady*

The pen tool would be my first choice itself. Could be very easy. or Very difficult.. There are many tut's online discribing the effect you are looking for..

Here's just one basic tut:
http://www.melissaclifton.com/tutorial-pentool2.html

turn of auto select, make sure the layer you want is selected, drag and drop

ONE point to bring up. Is there a little lock beside the image in the layer box on the right? If so you can't do much to it till you make a copy of the layer. So I'll presume it is there! Simply drag that box in the layer screen down to the white box at the bottom of that screen. When it hits release and you should now have 2 layers. The one at top with the blue tint is the now active one and is not locked. One thing is to click the eye on the locked one so it will be unseen.
So you can do anything to the new one. Which is an exact copy of the locked original.
And by doing this even if you goof seriously as you go the locked one at bottom stays untouched.

So now move onto the edit part:

When you've set up the crop line in place around the portion you want simply do a EDIT on top, copy! And then under EDIT again, paste. It will give you the image the dotted line(Marque) was around. But it can be copied into another image as well after the copy has been hit.
Click on the other image you want it in. So it is on the top of the pile and you are looking at it directly. Then hit paste from under Edit. It should appear in this other image and it will be in it's own layer.
Now i will assume you don't know about layers. The little screen to the right of the main screen. If it is on you will see

There is several ways to do that. You could use the Marque tool from tools 2'nd from top on left row. Called Lasso to free hand a line around any image.In the Lasso box there are 3 choices for beginner stay with plain lasso top pick. Just above that is the circles and box Marques.(That simple to make a circle or box around something.)
It's also called a cut and paste at least in principal. It then gives a copy of just the item the line was around.

Hope this helps!