The standard way to use it (for those who have never tried it) is to mix:
1/2 Hydrogen Peroxide 3%
1/2 tap water
Start with normal tongue scraping, then use a tongue brush or toothbrush, dip it in the mix, and apply to back of tongue. Gargling for a couple of minutes might also be a good idea.
As mentioned, I know this has been around for years & years, but even now in 2008 it seems to be the only thing that works, if just a little .... or what do ppl who have tried it say..?

Edit: when using Hydrogen Peroxide (H202) make sure to only use the 3% solution, and mix it with the same amount water, as described above.