Go to the next page:
http://www.dd-wrt.com/site/support/router-database
select your model and download the linux.bin image, instead following the manual way like setting up a tftp server with the image and configuring the redboot loader...
Download from here:
http://www.gargoyle-router.com/download.php
The fonflash binarys corresponding your operating system in my case I used:
fon-flash-linux.tar.gz
untar and flash selecting the software (ddwrt in my case) using the nice gui or via command line tool:
sudo ./fon-flash -i eth0 -c ddwrt linux.bin
Once run the line above, power cycle your router and wait some time to have it flashed.
