Okay, it looks to be a 2nd generation device which will require this driver:http://jbnote.free.fr/prism54usb/data/firmwares/3887/18.104.22.168/22.214.171.124.arm
Download the above file. Then, as root, copy it to /lib/firmware (and /lib/hotplug/firmware if it exists) with a different filename (isl3887usb_bare) :cp 126.96.36.199.arm /lib/firmware/isl3887usb_bare
cp 188.8.131.52.arm /lib/hotplub/firmware/isl3887usb_bare
At this point, I believe you should have all of the pieces in place to get the device functioning. It may require rebooting your system to get all modules and driver files working correctly. You can then check 'iwconfig' to determine if the device is functioning correctly (wlan0 and wmaster0 should appear along with lo and eth0).