That is one of the Linaro 12.11 images, which only has a couple of wireless chipset drivers compiled as kernel modules. It supports the Ralink rt2800usb driver (but you have to enable it by modifying /etc/modprobe.d/blacklist-ralink.conf and adding a '#' in front of the driver name) and the Realtek rtl8191su (I think?) driver, which is the driver for the Hardkernel WiFi dongle 2.
If you are using a wireless dongle with a different chipset from those listed above, you will need to rebuild the Linux kernel and select the drivers for your WiFi chipset. There is an excellent guide in the Ubuntu How-To's section of the forum:[GUIDE] Rebuilding Ubuntu Kernel (Optional Mali Overclock)
That guide can tell you how to rebuild the kernel. You will need to do the optional portion where it tells you that you can use 'make menuconfig' or 'make xconfig' to add any extra drivers that you need.
One more option is o update to the latest Ubuntu image (Ubuntu 13.04 + XFCE) and use mdrjr's kernel update script to update to the 3.8 kernel branch. This kernel branch has most, if not all, wireless chipsets selected as modules already, so you wouldn't have to rebuild the kernel.