I have an Asus WL-520GU wireless router connected to a cable modem that I use for wireless internet access in my apartment. I would like to set it up so that it provides two SSIDs: one secured and password-protected for my regular use, and a "guest" SSID that's unsecured but throttled to, say, 10% of the available bandwidth. What is the most straightforward way to do this?

I've been looking into DD-WRT and Tomato, both of which support my router. DD-WRT supports setting up multiple SSIDs using the GUI, but I don't know if it's possible to limit the bandwidth of each SSID independently; point #12 in this FAQ thread says it's not possible to limit by day or by MAC address, which is discouraging but not conclusive. Tomato allows bandwidth limits in its QoS settings, going by the screenshot here, but multiple SSID support is still experimental and it doesn't look like it will work with the encryption settings or bandwidth limits in the GUI.

I'd like to know a good way to do this which gives me the fewest opportunities for screwing up. I'm no stranger to the command line, if that turns out to be what's necessary, but if so, please explain what the commands are doing because I don't have a good mental model of what needs to happen to set this up.