If you followed the WRT54Gv5 guide then it tells you to download the latest generic micro image if that link doesn't work or if there is something newer. The VXWorks Killer utility is also on that page.

It isn't simple because the older routers ran Linux. The newer cost reduced models have significantly less memory and run VXWorks instead. You need to load that VXWorks Killer utility which will actually erase VXWorks + bootloader and put on the CFE bootloader used for Linux instead.

What DD-WRT image did you flash onto your WRT54Gv5? Did you do the steps regarding setting the MAC address?

As for actually using a WRT54G, I don't any more. I've got a bunch of Cisco IOS APs and a WLC.