Just found this article although I dont keep up on the Linksys firmwares looks like they have developed a flash image that overwrites the boot loader on v.5 WRT54G's and allows them to run DD-WRT micro edition.
http://linuxdevices.com/news/NS6352077661.html
http://www.dd-wrt.com/dd-wrtv2/index.php
http://linuxdevices.com/news/NS6352077661.html
http://www.dd-wrt.com/dd-wrtv2/index.php