This toolchain is based on GNU binutils and gcc and is released under the GPL by Microchip.
First check if there are packages available for your distribution. Source and binary packages for Mandriva are available on thispage. There is also the option of installing the Windows binaries provided by Microchip with Wine. The student version worked for me.
Otherwise here are instructions for compiling from sources:
Using the Microchip 16-bit libraries and headers
Because of their license, these libraries, headers, and linker scripts cannot be distributed separately. So you have to get them from an installation of the Windows binaries either native under Windows or made with Wine.
If you made a native installation of the Pic30 toolchain. You can also copy "include", "lib" and "support" directories from a Windows install of MPLAB C30, as well as the file "c30_device.info" into "/usr/share/pic30-support".
You can also configure the respective paths in the toolchain configuration dialog (see screenshot). You may still need to add libraries manually to your project for proper linking.