Since getting an Atheros card on the gumstix appears to be impossible, I've been looking at other possibilities to get mesh going. Mark pointed out that if necessary we can have 2 cards in the gumstix and we can have a usb hub (so we still get storage). The new approach is to use OLSRd on the gumstix for the mesh and write a few scripts/programs to scan for APs, associate with an AP if it connects to the internet and advertise that to everyone else or connect to a mesh node AP if there are no other options. All of this can be done with shell scripts or perl (or we can do it with Ruby like the Merakis, but perl seems easier).
Today I'm putting together everything necessary and hopefully gonna get a chance to try it out. I need hostapd (to run an AP) and olsrd (to run mesh). We're gonna stick with the prism2 cards and the hostap drivers, since if we can have an interface running an AP and an interface running in Managed mode, out problem is resolved.
A useful guide I found to OLSR: http://tldp.org/HOWTO/OLSR-IPv6-HOWTO/olsrlinux.html