For a bz2 file, you would use the bunzip2 command to uncompress it. For example, "bunzip2 library_IRIX.tar.bz " would create a file called "library_IRIX.tar".
tar is an old format that was originally used for archiving files to tape. On IRIX, use "tar tvf
filename.tar" to see the contents of a tar file, and then you can use "tar xvf
filename.tar" to extract the contents. For example, "tar xvf library_IRIX.tar". That will probably create a folder/directory called "library_IRIX", inside of which I guess you will find software that you can install.
You might sometimes see .tardist files. They are just regular tar files that happen to contain an installable software image. It is used only on IRIX systems. On some IRIX systems, clicking a link to a tardist file will open it in the Software Manager. On any system, you can use the tar xvf command to extract the installation files, and then you can work with them just like they were regular files.
Sometimes you'll see .tgz files. These are the same thing as .tar.gz files, i.e. tar files that have been compressed with gzip.
gz is a gzip file. On IRIX, you can use the gunzip command to decompress it. For example, "gunzip software_IRIX.iso.gz" will result in a file called software_IRIX.iso - which should be a regular iso file that you can easily use to burn a cd on a Mac or Windows, or Linux PC. If you use Windows, the freeware 7-Zip utility works well with tar, bz2, and gz files.
http://www.7-zip.org/