Linking SoXt fails with a multiply defined symbols error...

The version of Openmotif installed by Fink conflicts with Apple's X11 SDK. If you get errors like

ld: multiple definitions of symbol _vendorShellClassRec
/usr/X11R6/lib/libXt.dylib(Vendor.o) definition of _vendorShellClassRec
/sw/lib/libXm.dylib(VendorS.lo) definition of _vendorShellClassRec
ld: multiple definitions of symbol _vendorShellWidgetClass
/usr/X11R6/lib/libXt.dylib(Vendor.o) definition of
_vendorShellWidgetClass

uninstall Fink's openmotif package, download the Openmotif source and build it yourself (basic configure && make should work).