If your copy of Blender came from
the blender.org web site
, they suggest:
To install Blender, download the appropriate package for your platform to your computer. The Windows version comes with an optional self-extracting installer, for other operating systems you can unpack the compressed file to the location of your choice.
Provided the Blender binary is in the original extracted directory, Blender will run straight out of the box. No system libraries or system preferences are altered.
The IRIX Software Manager isn't needed. Decide where you'd like to install blender and untar the archive there - it will create it's own directory. The blender.org distribution is self-contained, it should run from where ever you decide to locate the expanded tar file.
As an example <assuming you have downloaded the most recent version of Blender from their web site>:
If the blender tar file is in your home directory,
tar -xvf blender-2.49a-irix-6.5-mips-py2.5.tar
That will create a directory named "blender-249a-irix-6.5-mips-py2.5"
Blender can then be run from inside that directory.