- Go to the dd-wrt website and then to the "Supported Hardware" tab (the downloads tab was way too arcane to navigate). Type in the name of your hardware (my case: wrt54gl)
- Download the "Mini-Build required for initial flashing via WEB." The other mini build didn't work for me and resulted in the lolcatesque error, "Upgrade are failed!" Also download the "Standard Generic" (I chose the non-usb one). See the picture for more info.
- Log into the router admin interface at 192.168.1.1 and flash the firmware with the mini build. If you aren't just pulling the router out of its box, you might want to hard reset and power-cycle the unit before this step.
- Hard reset and power-cycle the router, then upgrade the firmware again to the standard generic.
- Another hard reset and power-cycle should have the router up.
All in all, it was a pretty painless process once I horsed around with it for a few minutes. I also found some other references to be helpful: