emerge -va xorg-server
These are the packages that would be merged, in order:
Calculating dependencies... done!
[ebuild N ] media-libs/mesa-7.6.1 USE="nptl xcb -debug (-gallium) -motif -pic" VIDEO_CARDS="-intel -mach64 -mga -none -r128 -radeon -radeonhd -s3virge -savage -sis (-sunffb) -tdfx -trident -via" 4,773 kB
[ebuild N ] x11-base/xorg-server-1.6.5-r1 USE="hal ipv6 nptl xorg -debug -dmx -kdrive -minimal -sdl -tslib" 4,575 kB
[blocks B ] <x11-base/xorg-server-1.7 ("<x11-base/xorg-server-1.7" is blocking media-libs/mesa-7.6.1)
Total: 2 packages (2 new), Size of downloads: 9,347 kB
Conflict: 1 block (1 unsatisfied)
* Error: The above package list contains packages which cannot be
* installed at the same time on the same system.
('ebuild', '/', 'x11-base/xorg-server-1.6.5-r1', 'merge') pulled in by
xorg-server
For more information about Blocked Packages, please refer to the following
section of the Gentoo Linux x86 Handbook (architecture is irrelevant):
http://www.gentoo.org/doc/en/handbook/handbook-x86.xml?full=1#blocked