Try adding the following directories to your path: (Of course using the correct install directory for your 8.1 install..)
/opt/altera/11.1/quartus/sopc_builder/bin/:
/opt/altera/11.1/nios2eds/bin:
/opt/altera/11.1/nios2eds/sdk2/bin:
/opt/altera/11.1/nios2eds/bin/gnu/H-i686-pc-linux-gnu/bin:
Of course for longevity, I would try to migrate to the newest tools, but if that isn't possible, a Virtual Machine is a nice way to archive old projects. Generate a VM with Windows XP and all the tools you need, and build it in that. (Vmware player is free! and works great!)
Pete