Photoshop CS3 Tutorial
How to Distribute Shape Objects in Photoshop
If you have a series of shapes and need to space them evenly in the document, this technique is quite helpful.
It distributes the objects by calculating the distance between the object centers. For objects with varying widths, you'll find that the space between the objects can vary quite a bit.
Open a new blank document in Photoshop (File > New). Set the size to 500 pixels by 500 pixels and the resolution to 72 ppi.
Click the Rectangle tool and set the options to Shape Layer.
Use the Rectangle tool to draw three rectangles in the workspace.
With one layer selected, Cmd (PC-Ctrl) click the other two. All three shape layers should be selected.
Choose Layer > Distribute + Horizontal Centers.