Compiling 64bit programs

Hi there, I have a question: how can I compile 64bit programs under Splack? I can\'t understand what all the various GCC commands are for, but they all give some errors:
cclix7:~ $ gcc64 a.c
a.c:1:19: stdio.h: No such file or directory

cclix7:~ $ gcc -m64 a.c
cc1: -m64 is not supported by this configuration
cc1: -mlong-double-64 not allowed with -m64

What should I do? GCC is 3.2.3 (splack-current), and a.c is just a helloworld program.

Thanks in advance!