I have my desktop images set to change every 30 minutes in random order. Sometimes the desktop will display an image that displayed earlier in the day, and I wanted a way to 'advance' the image easily. The following AppleScript will cause the desktop image to change, in whatever order you have set, each time it is run:
property theSwitch : 0
if theSwitch = 0 then
tell application "System Events"
tell current desktop
set change interval to 1801.0
end tell
end tell
set theSwitch to 1
else
tell application "System Events"
tell current desktop
set change interval to 1800.0
end tell
end tell
set theSwitch to 0
end if
To maintain your current change interval, modify the change interval lines to reflect your interval, measured in seconds. Thus, for my 30-minute setting, I used 1801 and 1800 seconds. One hour would be 3601 and 3600, etc. For this script to work, you must have both Change Picture and Random Order enabled on the Desktop tab of the Desktop & Screen Saver System Preferences panel.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20080610081312728