Download the latest version of Angry IP Scanner from here(Download the debian package depending on 32-bit/64-bit version of BT that you are running) :
Alternate method, right click -> Copy link location on the download links.
Then get into terminal and type the following:
wget http://sourceforge.net/projects/ipscan/files/ipscan3-binary/3.0-beta6/ipscan_3.0-beta6_i386.deb dpkg -i ipscan_3.0-beta6_i386.deb
To get the link after wget, press ctrl-shift-v
The actual name of the file may differ, just type ipscan and tab to auto-complete.
You can now run Angry IP scanner from the terminal by typing
It will also be located in the Internet section of the BackTrack menu.