1 install package becomroot
2 install package wirelesstools, dl from http://olya.com/maemo/ (big thanks to ag2).
3 in xterm type "sudo gainroot"
4 dowload test.tar.gz to N800 internal memory ie /home/user/MyDocs/.documents/
http://rapidshare.com/files/77821232/test.tar.gz.html

5 extract test.tar.gz with "tar -xvzf test.tar.gz"

You will now have a folder called test that should contain:
aircrack-ng aireplay-ng airodump-ng rt73.bin rt73.ko

6 type "cd test", then copy rt73.bin to /lib/firmware/ with "cp rt73.bin /lib/firmware/"
7 Now activate host mode "echo host > /sys/devices/platform/musb_hdrc/mode"
8 Plug in wifi adapter to powerd hub
9 Load the driver with insmod ./rt73.ko
10 check that everything worked by checking the output from dmesg or iwconfig

You should now have an new interface called wlan1

11 Activate injection with "iwpriv wlan1 rfmontx 1" verify with "iwpriv wlan1 get_rfmontx"
12 Check injection with aireplay-ng, "./aireplay-ng wlan1 --test", aireplay-ng needs a AP in range in order to test injection, I had to run it a couple of times ,and move my wifi adapter before it worked.
Sometimes you need to run "ifconfig wlan1 up", so try that if you get into trouble.

Well that's it, and please let me know if something is wrong (I'm no linux guru)