I don't have the Vox with me and this is from memory, but I think it's right (or close to it).
From the Vox, you can use either
ES File Explorer or a
terminal emulator. ES File Explorer gives you a Windows-like folder browser and the terminal emulator gives you a linux shell.
From a terminal, "ls -a -l /system/bin/su" should show permissions (on the left) of "-rwsr-xr-x". If the "s" is an "x", then that would cause the problem. The "chmod 4755" command is responsible for that, so repeating the part of the directions that copy the su binary to the card would fix it. The other half is the SuperUser app, so if SuperUser (I think the app icon is the android robot with an eyepatch) isn't in your app list, then that's the problem.
Finally, it's supposed to ask you if you want to grant superuser access when something uses "su". It's possible to tell it "no" in a way that it denies access and never asks you again. To fix that, run "Settings" and go to the "Applications" tab. Find the SuperUser app and select "clear data".
If everything's working, you should be able to type "su" into the terminal emulator and it will pop up a window asking if the terminal emulator can have superuser access. Say "yes" and your prompt should change from "$" to "#".