If you bricked your router, there seems to be only one way (not counting JTAG) to get it back to life, which is the Windows-only tool you can download from the Netgear webpage. It exchanges raw Ethernet frames with the router to reflash and verify the flash contents.
To me this actually seems like a safer flashing method than the on-line flash in the web interface so I use it every time. The first part was actually written by someone known as rootkit on the OpenWRT forum, but never finished. Since upslug2 didn't work for me and seemed over-engineered, I tried to make nftp.c work instead, which wasn't too hard.
You can download it from here: http://wilmer.gaast.net/834root/downloads/nftp.c
Works on my DG834Gv4, should work on some other routers. There's some basic sanity check to see if the image is right for your router, but this check is just dumb guesswork. You probably want to remove the check, but do make sure you know what you're doing, you may end up breaking your router even more than it already was!