http://jcmc.indiana.edu/vol9/issue1/Japanese_Keyboard.gif
Try the ` button on the Right of the "P" Key.
Also, Vista/7 doesn't like the console very much. Maybe this might give an insight about it: http://fallout.wikia.com/wiki/Talk:Fallout_3_console_commands#Troubleshooting
Yes, my keyboard is very similar to that. I have read that other people with Japanese keyboards have been successful in using the ` button, but it didn't work for me.
Sadly, it says in that wiki link you provided that the console is not compatible with Windows 7. So I appear to be [censored] out of luck.
Thanks for your time!