First things first. These tutorials contingue to be popular, but please keep in mind that they were originally written in 2001/2002 and have not really been updated for later versions of Photoshop.
A few paramater changes to your Photoshop will help you to follow the tutorials.
All sizes in the tutorials are stated in pixels.
Edit>Preferences>Units & Rulers
Ctrl-R to view Rulers.
To see coordinates and measurements make sure the info window is visible:
Make sure you always have two guides on screen middle width and middle height. This will help centre elements on screen.
All images are created in RGB colour mode.
The tutorials have been executed in Adobe Photoshop 6.0, but most should also work in version 5 of the software.