do you have acpi working? if you run acpi in the console, what happens? You also may need to download the kernel patch for software suspend 2 from www.suspend2.net.
I believe that makes it easier to do a hibernate than the software suspend option in the kernel. You would then need to install the hibernate package(I don't know what distro you're using, in debian, the command would be 'apt-get install hibernate'). Hope this helps