Hi Malte,
I am sure, you know the Mac OS X specific definition:
ns_section "ns/server/${server}/modules"
...
ns_param libthread ${homedir}/lib/libthread2.6.1.dylib
...
A OS independent definition would be
ns_section "ns/server/${server}/modules"
...
ns_param libthread ${homedir}/lib/libthread2.6.1[info sharedlibextension]
...
Does this answer your question?