That's one of the reasons I'm turning on my guest network as well. I had planned on adding a second access point, but this is FAR easier (and you don't need Tomato in order to do it).

In my router's admin page you even get a few nice options to go along with it, and I can set up each band individually. If I don't choose any options, it essentially acts as a second network, putting all the people who connect on that SSID in their own bin that can't touch the main network, though people on that network can see each other. I then have the option to isolate users on the guest network so that they can't see each other. I can also go the other way and tell the router to let guest users see my content. I don't know why I'd do that, though, since I'd think the whole idea of having a guest network is to have a network separated from your stuff...

Anyway, I've enabled the guest network on both bands on my router, so I'll see how it goes