Please note before embarking on this adventure;
1) Opening your router’s casing instantly makes your warranty go *POFF*.
2) This is a reasonably technical article – if you don’t know how to solder cables to motherboards, don’t know how to set up a tftp server, don’t know what a terminal emulator is, can’t google to find out – then this article is not for you – it’s for people who are able to do what I’ve done and can understand what is going on. However, if you wish to learn, and know you will be capable of finding out how those tasks above are done, read on 
3) I take absolutely NO responsibility for any harm you may do to your hardware. None. Zip. Nada. What I outline here worked for me and still does. If you managed to burn down your house, or melt the Arctic ice cap, or flood your continent with the oceans, or any other disaster, then it was your fault for trying this and not mine. I didn’t ask you to, and this is for information purposes only for those interested.
So impressed was I with the specifications of this router that I just had to get it – even before I knew whether I could run alternate firmware on it or not – but I assumed that I would be able to. So having returned home with prized router in hand I proceeded to unpack it, plug it in and set it up.
I’m from the UK, but I now live and work in Japan. I’ve been studying Japanese for more than 2 years but I’m really not that cut out to learn the language – too many other interesting things to do – like tinker with shiny new hardware for example.
So the router powers up, and I get to its configuration page. Ugh. Default Buffalo firmware (of course). Not only that, it’s in Japanese (it being the Japanese model of course) but not only that no option to set it to English. How considerate – not.
Question to the router manufacturers… WHY IS YOUR STOCK FIRMWARE ALWAYS SO AWFUL!?!?! Ok, lets see if there’s dd-wrt support for it yet. Oh, a .tftp binary has been released for this model! Good. Oh it’s still a Work In Progress release (i.e. may contain many show-stopping bugs) but what the heck I’ll just upgrade the thing anyway because surely anything is better than the dreck which is lurking inside this router!
Downloaded, ok let’s follow the upgrade instructions – which are to power the router off, configure an ethernet port to 192.168.11.2, then run tftp, prepare that to send the image to 192.168.11.1, power up the router, send the image and them WHAMMO you have a nice shiny router with dd-wrt running on it and all my problems are over!
THINK AGAIN! “Hmm. This firmware is not installing. How… annoying.” After the umpteenth time performing this operation, it was time to go onto the dd-wrt forums and start asking questions. After about a week of that, and getting very little progress (I was still giving the Japanese Bufallo firmware blank stares), it was Time To Take Matters Into My Own Hands.
So, here’s the skinny on this Japanese model router. OK first thing I need is a serial console – how do I do that? There’s no serial interface on the unit I can simply plug into and go. There is however a serial interface on the motherboard – but its TTL level (3.3 volts) so I’d need to either build a TTL-serial converter circuit OR, and this is the nifty thing – I could by a conveniently available USB to TTL serial cable. Which has all the necessary electronics packed into the USB head, and the other end has 5 wires which I can use to solder onto the relevent motherboard connections.
That was that problem solved. So, armed with Ubuntu, a USB-TTL serial cable wired to the motherboard, and my knowledge, I decided to have a poke around the unit…
Sorry about that.