The following TWO (2) firmware versions should be downloaded in advance onto the PC that will be used for this operation:
1) The mini version used for the 1st flash: http://www.dd-wrt.com/routerdb/de/download.php?file=1190
2) The standard version used for the 2nd flash: http://www.dd-wrt.com/dd-wrtv2/downloads/others/eko/BrainSlayer-V24-preSP2/07-21-09-r12533/broadcom/dd-wrt.v24_std_generic.bin
The procedure for flashing is pretty straight forward. Toss the included CD and the sticker covering the back ports away. The CD is worse than useless anyway. You will need a standard straight-through CAT5 cable, which is the “regular” variety network cable. Connect the cable from a PC to one of the four LAN ports of the 54GL. Make sure that you don’t have any other connections (wireless or wired) by either unplugging other NICS or disabling the wireless card if it has one.
I don’t know how your PC is currently configured IP-wise, but most likely it’s getting a DHCP lease. So, open a command line (Start->Run), type in ‘cmd’ & hit OK. A good ole DOS box should open, the type in “ipconfig /release” (no quotes) followed by “ipconfig /renew” (no quotes). You should get an IP in the 192.168.1.0/24 subnet (probably 192.168.1.100). Alternatively, you can set a static IP using something within the 192.168.1.0/24 subnet, such as 192.168.1.2 (netmask 255.255.255.0 and gateway 192.168.1.1).
Back to the Start->Run and type in http://192.168.1.1 and hit OK. Should take you to the router login, which is a blank username and a password of “admin” (no quotes). Go to the Administration -> Firmware area. Having downloaded the DD-WRT .bin file(s) somewhere on this same machine, you will simply browse to it from within the firmware GUI and click apply or update. For the first time, use the mini version! You will re-flash afterwards to the standard. If you try to flash the standard version first, you will brick the router!
Now, this is important! Once it starts doing the upgrade, walk away! If you smoke like I do, go have a cigarette. Give it about 5 minutes. Wait for the device to re-flash itself and report complete. Don’t touch that Continue button. Just wait 5 full minutes.
Then unplug power from the router. Hold the reset button in with a pen or pencil while plugging power back in. Continue holding the reset button for 30 seconds. Let the router boot up once more (the power LED will stop flickering when it’s booted).
Now, fire up your browser and go to http://192.168.1.1 again. The newest build asks for a username and password reset before continuing. The older builds just brought up a login box which use a generic username & password combo of “root” and “admin” respectively. Get back into the administrative tab of the new interface and re-flash the firmware using the Standard version this time. Use the same procedure (smoke a cigarette while flashing, unplug & reset, etc.). Afterwards, you should be good to go!