I picked up one of these off eBay for testing a
Linksys WRT54GS v1.1 and installed dd-wrt on it.
Its a fantastic firmware modification.
I can now setup as many vlans as I want on both the LAN and WLAN interfaces.
Its also possible to put the wireless side of the device into client mode to create a bridge.
I am currently testing the OpenVPN aspect of box. Take a look at dd-wrt.com for more info.
Setup Guide is here.. http://www.dd-wrt.com/wiki/index.php/Installation