To be able to install most software to your own install of BackTrack 5 R2 that does not come from the repo's you will need to prepare the kernel sources.
This is very simple to do and will only take you a couple of minutes.
At the terminal, issue the following commands:
apt-get install linux-source
cp -rf include/generated/* include/linux/
And that's it.
Other than resolving any dependency requirements of the software you wish to install, you are now good to go.