So... let me state this. One if you do this you void your warranty. I will not help you in anyway if you brick your router nor will i help with issues on the firmware. I love dd-wrt, just not working on others. This is the one thing i am picky about.
You need to do the following.
log into the router with the bufpy/otdpopy[password] trick w
go to the firmware update page and upload the buffalo dd-wrt firmware.
After its done and you are able to loggin to the router. You need to do a factory reset to clear the memory. Once done you should be good to go.
I did this when it was on the released firmware for the router. And had no issue though to me, dd-wrt did not work very well.. or really that good at all. Reverted back to stock and there was a big difference of improvement.
Just letting you know. You lose like half your lan speed and wireless speeds. That what i lost