As predicted, the open-source community has come up with a way to convert VxWorks-based Linksys wireless WRT54G routers to Linux. The process does not require hardware hacking and installs a recent version of "DD-WRT micro." A version of Linux that supports the VxWorks-based "series 5" WRT54G has been available since April, when the DD-WRT project created its "micro" edition, with a 1.7MB footprint. However, the firmware could only be installed on routers modified to expose their JTAG ports (complicated instructions here).
Now, Jeremy Collake, aka "db90h," appears to have created a "VxWorks Killer" flash image that overwrites the VxWorks bootloader on series 5 WRT54G routers with normal Broadcom CFE firmware. This then enables the device to be put into maintenance mode at startup, after which Linux firmware can be installed easily.