Scripting from a USB Volume

Hi

Firstly, forgive me if this is in the wrong place.

I have created a simple apple script (my vary first one) in which I wanted the script, when run, to open a random image from a folder that had images within it. I did it using this code:

tell application "Finder"

(* get a random image file from a desktop folder *)

set randomImage to some file of folder "Pictures"

openrandomImage

end tell

That worked well and good when the folder containing the images was on the desktop. However, the folder I really want to use is on a USB stick. How can I tell the script that the folder I want it to run with is on the USB Stick?

I know I could easily copy the folder from the stick to the desktop, but I'd rather keep the folder on the stick.

Vary many thanks.