i did not try vde yet as i don't have debian-chroot installed atm. Setting the wlan0 to ad-hoc however basically works like this:

iwconfig wlan0 mode ad-hoc
ifconfig wlan0 [ip adress]
iwconfig wlan0 essid [name]

for testing this should do, have not yet tried to connect with another machine though.

misses encryption and dhcp server, so connecting hosts need to have a fitting manual ip setup