From DD-WRT Wiki
(K)ubuntu Linux Client Install for standard build on WRT54GL v1.1
0. Install Chrome. Firefox will not work in the second install. See http://www.ubuntu-inside.me/2009/06/google-released-google-chrome-not.html
0.1 I have a static on my client so I turned off network manager (sudo pkill NetworkManager)
0.2 Download your target firmware. In my case, ftp://dd-wrt.com/others/eko/V24_TNG/svn12548/dd-wrt.v24-12548_NEWD_mini.bin and ftp://dd-wrt.com/others/eko/V24_TNG/svn12548/dd-wrt.v24-12548_NEWD_std.bin
0.3 WRITE DOWN all your current routing settings. In my case, I took about 30 screenshots for this purpose.
1. Reset the router Press reset and hold for 30s, then power off for 30s with the reset still pressed, and then power on with reset held for 30s [30/30/30 reset]
2. Upgrade to dd-wrt.v24-12548_NEWD_mini.bin using the the web firmware update facility. I used Firefox, but Chrome will probably work as well.
3. Do another 30/30/30 reset
4. Using Chrome (Firefox will not work - it will give a timeout error), use the web firmware update facility in dd-wrt to the standard build, in my case dd-wrt.v24-12548_NEWD_std.bin
5. Do one last 30/30/30 reset
6. Access your web interface and restore your settings from 0.3
I hope this helps someone :)