this script is going to make your installation a mess in my opinion.
1) gstfarsight and farsight2 are installed with make install command. Thats not acceptable in a standard debian system. You should create a deb package and then install it with dpkg -i. You can easily create deb packages from any source if instead make install you type checkinstall (if you apt-get it first of cource).
2) farsight2 and gst farsight are already available for hardy as deb packages, from the telepathy ppa repository! No need to install anything from source or create packages! See here: https://launchpad.net/~telepathy/+archive
[ unfortunatelly, the gstfarsight version is the previus one, and does not include siren. We can ask/upload the new version, or just create the package with checkinstall locally ]
3) You install amsn with the 'make install' command. The whole reason that the 'make deb' command exists, is so that you can create a nice deb package and install it, so that you can easily uninstall it when you want.
These 3 points come from a very fast examination of your script, unfortunatelly i dont have time to examine it more.
I would NOT suggest it to anyone, since it will mess up the installation.
Its a common/best practice in debian based systems, that 'if something exists/can be install as a .deb package, the do it' instead of installing from source.
If we needed to install from source everything, we would run gentoo... :>
Appart from all these, if you change your script a little, to avoid the 'direct' installations, make deb package for amsn, and install the pre-built farsight .deb files, then it would be a nice script to use, that doesn't mess up a users system.