OK, there's an update to this. I brought the device back to work today from configuring it at home last night, and now wireless hosts can see each other on the newtork. Not sure why this has occurred. I'm assuming the rest of my config is OK, since the hosts are getting DHCP addresses and are able to communicate. Some kind person on another forum suggested that "ACL 100 is inbound to the router from the internal LAN, and this statement
access-list 100 deny ip host 255.255.255.255 any
is causing the problem I think." I have since permitted this on the access list. Any other help is appreciated, as I'm pretty much a Cisco noob. BTW, when I did the SDM express set up, I checked the box that pre-setup the firewall.