I tested everything on an ASUS WL-500GD and a user has reported that it also works on an ASUS WL-500G Premium v.1. The project contains an customised OpenWRT kernel (2.4 or 2.6)  (which will boot from an USB-disk or USB-stick) and an Debian Etch GNU/Linux pre-installed base image, which includes a lot of customisation. The image contains pre-configured out-of-the-box enabled networking, firewall, webserver, Samba server, and more.

Unfortunately there are some issues(see the project pages) with the b43 wireless driver and the 2.6 kernel, so for that reason I created also a 2.4 kernel image with full wireless support.

See the project website http://www.debwrt.net/ for more information. Also if you are interested in how to compile a custom OpenWRT kernel, or how to create an Debian base root filesystem for an embedded device from scratch.