compiling multithreaded apps

[Bryan]

I have a new Intel Core Duo, and I notice that many of the apps I use
seem to favor only one processor.  If I built an app with gcc, can I
make compile an app so that it utilizes both processors, or am I out
of luck?

I googled around and that I found this site:

http://altinity.blogs.com/dotorg/2004/08/gcc_compiler_op.html

by using the "-j" switch in conjunction with make, I can make gcc use
all available processors, reducing compile times.  But I have found
nothing about whether you can compile to allow for an app to be
multi-threaded, or single-threaded...

Any help is appreciated...

Bryan