Tried to rebuild sussen with these flags:

[ebuild  N    ] net-analyzer/sussen-0.90  USE="-debug doc gnome" 0 kB 

Fails:

[...]
 i686-pc-linux-gnu-gcc -DHAVE_CONFIG_H -I. -I. -I../../.. -I../../.. -march=pentium-m -O2 -pipe -fomit-frame-pointer -MT interface.lo -MD -MP -MF .deps/interface.Tpo -c interface.c  -fPIC -DPIC -o .libs/interface.o
if /bin/sh ../../../libtool --mode=compile i686-pc-linux-gnu-gcc -DHAVE_CONFIG_H -I. -I. -I../../.. -I../../..    -march=pentium-m -O2 -pipe -fomit-frame-pointer -MT rpm.lo -MD -MP -MF ".deps/rpm.Tpo" -c -o rpm.lo rpm.c; \
        then mv -f ".deps/rpm.Tpo" ".deps/rpm.Plo"; else rm -f ".deps/rpm.Tpo"; exit 1; fi
 i686-pc-linux-gnu-gcc -DHAVE_CONFIG_H -I. -I. -I../../.. -I../../.. -march=pentium-m -O2 -pipe -fomit-frame-pointer -MT rpm.lo -MD -MP -MF .deps/rpm.Tpo -c rpm.c  -fPIC -DPIC -o .libs/rpm.o
In file included from rpm.c:3:
/usr/include/rpm/rpmlib.h:11:20: error: rpmtag.h: No such file or directory
/usr/include/rpm/rpmlib.h:12:24: error: rpmversion.h: No such file or directory
In file included from rpm.c:3:
/usr/include/rpm/rpmlib.h:122: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'rpmHeaderFormats'
/usr/include/rpm/rpmlib.h:264: error: expected ')' before 'first'
/usr/include/rpm/rpmlib.h:291: error: expected declaration specifiers or '...' before 'Header'
[...]

I'll attach the complete build log.

Is that because of some incompatibility with RPM 5.0? I have that installed with the following flags:

[ebuild   R   ] app-arch/rpm-5.0.0  USE="berkdb -bzip2 -doc -file -lua -neon nls pcre -perl python (-selinux) -sqlite" 0 kB 

--($:~)-- emerge --info
Portage 2.1.4_rc14 (default-linux/x86/2007.0/desktop, gcc-4.2.2, glibc-2.7-r1, 2.6.23-gentoo-r1.r08.mit-ide-mod_2 i686)
=================================================================
System uname: 2.6.23-gentoo-r1.r08.mit-ide-mod_2 i686 Genuine Intel(R) CPU T2400 @ 1.83GHz
Timestamp of tree: Tue, 08 Jan 2008 08:46:01 +0000
distcc 2.18.3 i686-pc-linux-gnu (protocols 1 and 2) (default port 3632) [disabled]
ccache version 2.4 [enabled]
app-shells/bash:     3.2_p33
dev-java/java-config: 1.3.7, 2.1.3
dev-lang/python:     2.4.4-r4, 2.5.1-r5
dev-python/pycrypto: 2.0.1-r6
dev-util/ccache:     2.4-r7
sys-apps/baselayout: 1.12.10-r5
sys-apps/sandbox:    1.2.18.1-r2
sys-devel/autoconf:  2.13, 2.61-r1
sys-devel/automake:  1.4_p6, 1.5, 1.6.3, 1.7.9-r1, 1.8.5-r3, 1.9.6-r2, 1.10
sys-devel/binutils:  2.18-r1
sys-devel/gcc-config: 1.4.0-r4
sys-devel/libtool:   1.5.24
virtual/os-headers:  2.6.23-r3
ACCEPT_KEYWORDS="x86 ~x86"
CBUILD="i686-pc-linux-gnu"
CFLAGS="-march=pentium-m -O2 -pipe -fomit-frame-pointer"
CHOST="i686-pc-linux-gnu"
CONFIG_PROTECT="/etc /usr/kde/3.5/env /usr/kde/3.5/share/config /usr/kde/3.5/shutdown /usr/share/config"
CONFIG_PROTECT_MASK="/etc/env.d /etc/env.d/java/ /etc/fonts/fonts.conf /etc/gconf /etc/php/apache2-php5/ext-active/ /etc/php/cgi-php5/ext-active/ /etc/php/cli-php5/ext-active/ /etc/revdep-rebuild /etc/terminfo /etc/udev/rules.d"
CXXFLAGS="-march=pentium-m -O2 -pipe -fomit-frame-pointer"
DISTDIR="/Gentoo/Portage/distfiles"
EMERGE_DEFAULT_OPTS="--alphabetical"
FEATURES="buildpkg ccache collision-protect distlocks metadata-transfer parallel-fetch sandbox sfperms strict unmerge-orphans userfetch"
GENTOO_MIRRORS="        http://ftp.heanet.ie/pub/gentoo/        http://ftp.gentoo.or.kr/        http://distfiles.gentoo.org/    http://www.ibiblio.org/pub/Linux/distributions/gentoo "
LANG="de_CH.UTF-8"
LINGUAS="de"
MAKEOPTS="-j3"
PKGDIR="/Gentoo/Portage/packages"
PORTAGE_RSYNC_OPTS="--recursive --links --safe-links --perms --times --compress --force --whole-file --delete --delete-after --stats --timeout=180 --exclude=/distfiles --exclude=/local --exclude=/packages --filter=H_**/files/digest-*"
PORTAGE_TMPDIR="/Gentoo/Portage/build"
PORTDIR="/Gentoo/Portage/tree"
PORTDIR_OVERLAY="/Gentoo/Portage/local-tree/misc"
SYNC="rsync://winds02:10873/gentoo-portage"
USE="X acpi alsa berkdb bitmap-fonts bluetooth cairo cdr cli cracklib crypt cups dbus dmi doc dri dvd dvdr dvdread encode fam firefox fortran gdbm gif gnome gnutls gpm gstreamer gtk hal iconv isdnlog jpeg kde kdeenablefinal kdehiddenvisibility ldap libnotify mad midi mmx mp3 mpeg mudflap ncurses nls nptl nptlonly ogg opengl openmp pam pcmcia pcre pdf perl png pppd python qt3 qt3support qt4 quicktime readline reflection samba sdl session spell spl sse sse2 ssl svg tcpd tiff truetype truetype-fonts type1-fonts unicode vorbis wifi win32codecs x86 xine xinerama xml xorg xv zlib" ALSA_CARDS="hda-intel intel8x0 intel8x0m usb-audio usb-usx3y" ALSA_PCM_PLUGINS="adpcm alaw asym copy dmix dshare dsnoop empty extplug file hooks iec958 ioplug ladspa lfloat linear meter mulaw multi null plug rate route share shm softvol" APACHE2_MODULES="actions alias auth_basic authn_alias authn_anon authn_dbm authn_default authn_file authz_dbm authz_default authz_groupfile authz_host authz_owner authz_user autoindex cache dav dav_fs dav_lock deflate dir disk_cache env expires ext_filter file_cache filter headers include info log_config logio mem_cache mime mime_magic negotiation rewrite setenvif speling status unique_id userdir usertrack vhost_alias" APACHE2_MPMS="worker" CAMERAS="ptp2 directory" ELIBC="glibc" INPUT_DEVICES="evdev keyboard mouse synaptics" KERNEL="linux" LCD_DEVICES="bayrad cfontz cfontz633 glk hd44780 lb216 lcdm001 mtxorb ncurses text" LINGUAS="de" USERLAND="GNU" VIDEO_CARDS="nv nvidia vga none"
Unset:  CPPFLAGS, CTARGET, INSTALL_MASK, LC_ALL, LDFLAGS, PORTAGE_COMPRESS, PORTAGE_COMPRESS_FLAGS, PORTAGE_RSYNC_EXTRA_OPTS