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Much to the dismay of many, the Chooser is not scriptable. But thanks to scripting additions, there is a way to work around it. Look into the freeware S√?¬§ndi's Additions, which includes the command "type text" and allows simulated typing on the keyboard.
Suppose you wanted to choose a printer named "LaserWriter Select 360" in the Chooser.
tell application "Finder"
open file ((path to apple menu items folder as text) & "Chooser")
type text "L" -- selects the LaserWriter 8 icon
type text tab -- move to the printer choices
type text "LaserWriter Select 360 " -- selects the driver
type text "q" holding down command -- quit the Chooser
type text return -- to okay the choice
The printer has been chosen!