--- configure.ac	2007-07-30 02:28:12.000000000 +1000
+++ ../configure.ac.new	2007-08-19 09:19:39.000000000 +1000
@@ -76,10 +76,16 @@
    fi
 fi
 
-AC_CHECK_HEADER(fftw3.h,
-   AC_CHECK_LIB([fftw3], fftw_execute,,
+AC_ARG_WITH([fftw],
+	    [  --with-fftw             use fftw3],
+	    [with_fftw=$withval],
+	    [with_fftw="no"])
+if test "$with_fftw" = "yes"; then
+AC_CHECK_HEADER([fftw3.h],
+   AC_CHECK_LIB([fftw3], [fftw_execute],,
            AC_MSG_NOTICE([*** Could not find libfftw3: will compile without optional fast Fourier transforms. ***])),
      AC_MSG_NOTICE([*** Header file fftw3.h not found: will compile without optional fast Fourier transforms. ***]))
+fi
 
 GCVERSION=gc-7.0
 
@@ -108,7 +114,8 @@
       then INCL="-I$prefix/include/gc" 
       else INCL="-I$ac_cv_use_gc/include/gc"
       fi
-      AC_CHECK_HEADER(gc.h,
+	
+      AC_CHECK_HEADER([gc/gc.h],
 	AC_CHECK_LIB([gc],[GC_malloc],[
 	  LIBS=$LIBS"-lgc "
 #	  LIBS=$LIBS"-lgccpp -lgc "
@@ -183,11 +190,17 @@
 		   [Define if you have a working <rpc/rpc.h> header file])],
    AC_MSG_WARN([*** Broken rpc headers; XDR support disabled ***]))
 
+AC_ARG_WITH(gsl,
+	    [  --with-gsl              use gsl libraries],
+	    [with_gsl=$withval],
+	    [with_gsl="no"])
+if test "$with_gsl" = "yes"; then
 AC_CHECK_HEADER(gsl/gsl_sf.h,
    AC_CHECK_LIB([gsl], gsl_sf_Si, [AC_DEFINE(HAVE_LIBGSL, 1,
    [Define to 1 if you have the 'gsl' library (-lgsl). ]) LIBS=$LIBS"-lgsl -lgslcblas "],
            AC_MSG_NOTICE([*** Could not find libgsl: will compile without optional special functions. ***]),[-lgslcblas]),
      AC_MSG_NOTICE([*** Header file gsl_sf.h not found: will compile without optional special functions. ***]))
+fi
 
 # Checks for typedefs, structures, and compiler characteristics.
 AC_TYPE_PID_T