Hmm, that's strange that it's not working for you.
Now that you mention it, I did install the Jailbreak as detailed in the screensaver & fonts hack thread
in order to get the screensaver hack working. Maybe that makes a difference?
My Kindle OS is v3.0.2, but I haven't installed any preview versions or anything.
You might try running the installer again? (i.e. when logic fails, use voodoo!)