If you want to set the printer preset from the terminal in 10.6 (or from an AppleScript via a 'do shell script' command), it's different than how it's done in previous versions of OS X.
Assuming you have a printer called 'Copy Room Printer' and a preset called 'double-sided, stapled,' you would run the following two commands:
defaults write com.apple.print.custompresets.forprinter.Copy_Room_Printer com.apple.print.lastPresetPref 'double-sided, stapled' defaults write com.apple.print.custompresets.forprinter.Copy_Room_Printer com.apple.print.lastPresetPrefType 3
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