If you look in /usr/portage/profiles/ you should be able to find make.defaults that your profile will inherit. They are split into multiple parts - e.g. architecture, kernel, desktop/server choice etc.
You can mask pciutils-3.1.8 which will fix things in the short-term. Long-term, you will find that software will depend on tools that don't work with hal, or require programs that conflict with it.
If you desire to keep using deprecated software (hal, kde3), it might be easiest to never update?
1) The display manager is the "desktop greeter" that runs when you turn on the computer, whereas the XSESSION specifies the desktop environment that will be run when you log in (via the display manager).
2) Under normal circumstances, xorg.conf is no longer needed as X does the necessary auto ...
For these types of errors (failing to find some library), `revdep-rebuild` is often the solution - as it will rebuild the packages that should link against newer versions of libraries.
It is possible that there was an incorrect dependency somewhere, so a package was emerged before all its dependencies were. Without knowing details, it is impossible to tell
It seems that you are mixing up different version of KDE on your system (4.6 and 4.7). Could you paste the output of your /etc/portage/package.keywords file?
Have you looked at http://www.gentoo.org/proj/en/desktop/kde/kde4-guide.xml - it has instructions on what needs to be placed in package ...