MAC Monitors, OS 10 or higher:
In the top menu bar >
select the Apple symbol on far left >
choose System Preferences dialog box >
second row from top choose Displays >
in Displays dialog box, under Display and
Resolutions, the highlighted dimension is your
current monitor size!

Download you choice of screen saver, save to your computer and use the Desktop & Screen Saver icon
in the top row of System Preferences to change your desktop image...that is it!

PC Monitors, Windows XP:
Right click in the center of your desktop and choose
Display Properties > in the lower left of the
dialog box is the Screen Resolution (which may
be changed by moving the slider, if you wish in
increase or decrease the pixel sizes)

Download you choice of screen saver, save to your computer and use the same Display Properties
dialog box, selec the Desktop tab to change your desktop image!