You can download a flash image which boots from a connected USB device here. If this image is flashed into the router, it'll try to use a connected usb storage device as a root filesystem.

A root-filesystem to boot the router off is downloadable here. Instructions on how to use it are below, though Dutch readers might want to check out this and this.

Features:

• Built-in webserver: thttpd
• Built-in bridge: All 5 Ethernet-ports will be tied together to form a 5-port switch. It won't matter which port you plug the cable in to communicate with the router. There's one exception: DHCP responses are only accepted on the 4 LAN-ports, the client somehow doesn't listen on the WAN-port.
• Telnet access (user=root, no password, just press enter)
• IP is fetched by DHCP
• Boot-time (from flash-like storage): 15 seconds

Installation guide: Needed: a Linux-workstation (you might get away by downloading and booting off a Knoppix CDROM, so you won't have to touch your HD) and an USB-mass-storage device (USB-pen, cardreader+flashcard, USB hard disk, ...) which doesn't contain data that shouldn't be erased

Use a root-login on your Linux-machine:

• Go to a console of your Linux-machine: press ctrl-alt-f1
• Connect the USB-device to an USB-port
• Some messages start scrolling over the screen. Look at the top one looking like this: SCSI device xxx xxx is 'sda' on my machine, that can be different on yours, if it is replace all occurences of 'sda' in this tutorial with your value. Be warned: if you use the wrong value you could destroy the data on any scsi devices or already plugged-in USB storage devices you have.
• Create a partition: enter: fdisk /dev/sda
• Delete existing partitions: press d and then enter until fdisk complains there are no more partitions to be deleted.
• Create a new partition: enter

  n p 1 enter enter

• Write the partition table to disk: press w and enter.
• Create the file system: enter mke2fs /dev/sda1
• Mount the fs: mount /dev/sda1 /mnt
• Extract the root fs mentioned above:
  cd /mnt
  tar -xjf /where/you/put/the/file/rootfs.tar.bz2
  
• Umount & disconnect:
  cd /
  umount /mnt
  and wait few moments for the prompt to return.