Getting the right version installed

Hi, I've just installed 64studio from my Athlon64 computer, but I have a feeling it's the 32bit version that has been installed. In the Synaptic manager only nvidia-kernel-2.6.21-1-multimedia-486 shows up, where according to http://64studio.com/faq_user , there should be a nvidia-kernel-2.6.21-1-multimedia-amd64 available, the repositories I have enabled are: sarge, etch, 64studio stable and beryl (though beryl is not set up yet). How do I find out what system I have set up? I'm new to the Debian system having used Gentoo over a year now so I am used to having more control during the setup phases of the system. Thanks