[Boost-users] "Compiler threading support not turned on" error

I'm attempting to use Boost.threads on Mac OS X 10.3 and am getting the error "Compiler threading support is not turned on" when trying to compile. I'm using Xcode, which is Apple's IDE, so I'm not sure what to do when the error text helpfully suggests I set the correct command line option. As far as I know, there's nothing extra that you have to do to enable threading support in the compiler. I've written multi-threaded apps using pthreads and never had to deal with command line options. Any suggestions? Thanks, Glen Simmons