want to set up a guest wireless network

I manage a network at our corporate office.  Basically we have corporate computers that connect to our lan through wired connections.  However, we occasionally have guests come that need wireless access and just to the internet.  I don't want them to have access to anything else on our network.  I have a cisco 1100 series access point that I'd like to use for the wireless guest access.  In addition, we have a cisco asa 5510 firewall.  The firewall has 4 interfaces aside from the management interface (outside, inside, backup internet line, and unused).  I was thinking of putting the cisco 1100 ap on the unused interface on the asa firewall and setup the firewall to perform dhcp on that interface of course setting up a different ip subnet on that interface.  I briefly played around with this but wasn't able to get this to work.  I heard some people mentioning using vlans to do this type of thing  as well.  Since I don't do this type of thing on a daily basis, I wanted to get some assistance as to what might be the best way to do this and how to do it.  I attached parts of the asa config.  Please send some advice.  Thanks!
cisco-asa.txt