This one works works with AppleScript-Editor & ScriptDebugger, give it a try.
-- MacIntel MBP13, OS X 10.6.2, QXP 7.5
-- AppleScript-Editor 2.3, AppleScript 2.1.1 (118)
-- ScriptDebugger 4.5.3
--
tell application "QuarkXPress Passport"
set vBoxRef to a reference to generic box 1 of document 1
set {y1, x1, y2, x2} to bounds of vBoxRef as list
set x1 to (coerce x1 to real)
set y1 to (coerce y1 to real)
set x2 to (coerce x2 to real)
set y2 to (coerce y2 to real)
set vWidth to x2 - x1
set vHeight to y2 - y1
end tell
{x1:x1, x2:x2, y1:y1, y2:y2, vWidth:vWidth, vHeight:vHeight}