Epson Perfection V500 - Manual (Page 178)

In the Select an event list, choose the button to which you want to assign a program.
In the Start this program list, choose the program you want to assign. Only compatible
programs appear in the list.
Note:
If you want to be given a choice of programs whenever you press the selected
button, click the Prompt for which program to run button instead. If you want
to disable the button from opening a program, click the Take no action button
instead.
Click Apply, then click OK.
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Assigning a Program With Windows 2000
Click Start > Settings > Control Panel.
Double-click the Scanners and Cameras icon.
Select your scanner and click Properties.
Click the Events tab.
In the Scanner events list, choose the button to which you want to assign a program.
In the Send to this application list, click the checkbox for the program you want to
assign. Only compatible programs appear in the list.
Note:
If you want to be given a choice of programs whenever you press the selected
button, select more than one program in the list. If you want to disable the button
from opening a program, click the Disable device events checkbox instead.