If you search @ msdn.microsoft.com for "autorun usb", you'll see that it is possible to associate apps to removable drives for autorun if you're using Autoplay V2 (embedded in WinXP). I guess (!) that PenDrive Autorun associate itself with removable USB drives and if an USB drive is added to the system and XP is polling what application likes to autorun, PenDrive Autorun says 'yes' if autorun.inf is found. So WinXP gives the control to PenDrive Autorun and PenDrive Autorun executes the file specified in autorun.inf. But that is only a guess. If it's true, than it's not possible to trigger an autorun from the USB, so only if PenDrive Autorun (or something like it) is installed on the computer, the trick will work.