This tutorial will teach you basic alignment techniques used in Photoshop. I could only test this in Photoshop 7, so I am not sure if it works for 6 or not. We will discuss both the hard way, and the easy way of alignment. You will find these incredibly useful when creating images in Photoshop when you need to align objects on the stage.

[ without alignment | vertical alignment | verticle+horizontal alignment ]

The "Secret" of Alignment
The following steps will help you learn how to align objects in Photoshop:

1. First let us get acquainted with the tools we will be using for this.
   
   = Marquee Tool
   = Move Tool
    
2. The first step to aligning in Photoshop is to use the Marquee Tool from the tools panel and select the area you will want to align your object to. I usually use CTRL+A to select the whole canvas, but you can use the marquee to select smaller areas, just make sure the object you want to align falls within the marquee you create. Now click on the layer that contains the object you want to align. For the final step, go to Layer/Align To Selection and choose the option you want.
   
    

   
   
   
    

    

3. What each thing does should be self-explanatory so I am going to leave that at that and say we just completed the "hard" way of aligning in Photoshop, now let's get to the easy way. (Please note that hard and easy is dependant on personal preference)
    
4. Ok, use CTRL+A to select the canvas (or the Marquee tool), Now select the Move Tool from the tools panel. You will see a panel towards the top of the screen that displays the tools available options. It will look like this (Please excuse the scaling down)...
   
    

   

    

5. Now you can use the tools highlighted in the image above to align your image to your selection. Here are enlarged examples of what these tool buttons actually look like and what they do.
   
   - Align Top Edge of Selection
   
   - Align Vertical Center of Selection
   
   - Align Bottom Edge of Selection
   
   - Align Left Edge of Selection
   
   - Align Horizontal Center of Selection
   
   - Align Right Edge of Selection
   
    

Tah Dah! That is all there is to learning how to align to a selection in Photoshop!