I emerged and can run vnstat with no problems on amd64. Please add "~amd64" to the keywords for net-analyzer/vnstat-1.4.
Oh, I forgot to attach my emerge info: Portage 2.0.50-r8 (default-amd64-2004.0, gcc-3.3.3, glibc-2.3.4.20040605-r0, 2.6.7-gentoo-r8) ================================================================= System uname: 2.6.7-gentoo-r8 x86_64 5 Gentoo Base System version 1.5.1 Autoconf: sys-devel/autoconf-2.59-r4 Automake: sys-devel/automake-1.8.5-r1 ACCEPT_KEYWORDS="amd64 ~amd64" AUTOCLEAN="yes" CFLAGS="-O2 -pipe" CHOST="x86_64-pc-linux-gnu" COMPILER="gcc3" CONFIG_PROTECT="/etc /usr/X11R6/lib/X11/xkb /usr/kde/2/share/config /usr/kde/3.2/share/config /usr/kde/3/share/config /usr/lib/mozilla/defaults/pref /usr/share/config /var/qmail/control" CONFIG_PROTECT_MASK="/etc/gconf /etc/terminfo /etc/env.d" CXXFLAGS="-O2 -pipe" DISTDIR="/usr/portage/distfiles" FEATURES="autoaddcvs ccache sandbox" GENTOO_MIRRORS="http://open-systems.ufl.edu/mirrors/gentoo/ http://gentoo.ccccom.com ftp://gentoo.ccccom.com http://mirror.datapipe.net/gentoo http://mirror.datapipe.net/gentoo http://gentoo.eliteitminds.com" MAKEOPTS="-j3" PKGDIR="/usr/portage/packages" PORTAGE_TMPDIR="/var/tmp" PORTDIR="/usr/portage" PORTDIR_OVERLAY="" SYNC="rsync://rsync.gentoo.org/gentoo-portage" USE="X aim alsa amd64 apm avi berkdb bonobo cdr crypt cups dvd dvdr emacs encode esd foomaticdb gdbm gif gnome gpm gtk gtk2 gtkhtml guile imagemagick imap imlib java jpeg kde libg++ libwww mikmod motif mozilla mpeg multilib mysql ncurses nls nogcj offensive oggvorbis opengl pam pda pdflib perl png ppds python qt quicktime readline samba sdl slang snmp spell ssl tcltk tcpd truetype usb xml2 xmms xv zlib"
In CVS now, thanks!