Flash your WRT54G or WRT54GS v5 series (v5, v5.1, v6)
From DD-WRT Wiki
 For the WRT54G v5, v5.1, and v6 ONLY
 For the WRT54GS v5, v5.1 and v6 ONLY
SERIOUS WARNING -- NO REVERSION TO VXWORKS ON THESE UNITS: At the moment for WRT54GS units this is a one way operation. No reversion back to VxWorks is available. I never got around to creating the GS reversion firmware. It could EASILY be created by someone using the tools I've written and the documentation here. A person once sent me a GS router hoping I might, but I didn't get to it and now no longer have that router. If someone would like to send me another GS unit, I will maybe get around to creating the reversion firmware. Also, if you'd like to donate other routers, feel free. Note that I make absolutely no guarantees that I'll complete anything though.
Copied from Bitsum
 Links to v5 and v6 Flash Instructions
 Enable 16 MB RAM
ATTENTION: WRT54gS ONLY!!!!! Doing this in your WRT54G will BRICK your router!