If you want to compile PAR2 with multicore support on Linux, it may not work right away from source. I used this version of PAR2 with multicore support. Update 2015: the original link is dead, I foud a copy of the source and put it on my own site here for you to download.
First, make sure that you have these libraries on your system:
According to this source, after downloading the source, you need to add this line:
To these files:
par2cmdline.cpp commandline.cpp par2creator.cpp par2repairer.cpp
Then edit the Makefile and find the LDADD variable. Add the -lrt option like this:
LDADD = -lstdc++ -ltbb -lrt -L.
This did the trick for me and compiled the PAR2 source with multicore support. Hope it helps somebody.
If you want to use Multicore PAR2 with SABNZBD you need to go to the Config menu. Then select 'Special' and enable 'par2_multicore'. Save the changes. Then go to 'Switches' and enter '-t+' at the Extra PAR2 Parameters field.