2011-12-18.

Using -- briefly at least -- the newer Gentoo (2011-08 KDE4.7, rather than 2009-09 KDE3.5).
vmwares are all masked now in Gentoo.

Wondering about the best option for doing emulation: sometimes useful, e.g. for packages
that run easily in a Fedora or Ubuntu but create hassle for Gentoo.

KVM seems suitable: it uses the virtualisation support of modern processors,
and the kernel contains (since ages ago -- ~2.6.20) support for this.
It's [claimed somewhere as] the core of RedHat's non-xen virtualisation, and
I know I was happy with that even several years ago (on "fluxim" server).

E.g.  http://en.gentoo-wiki.com/wiki/KVM

The command and (optionally) GUI interface for this is qemu-kvm:
http://en.gentoo-wiki.com/wiki/QEmu

This has a lot of options, and looks rather clever, e.g. ability to be a real 
emulator of different CPUs if wanted (not for our case).

[ebuild  N     ] app-emulation/qemu-kvm-0.14.1-r2  
USE="aio alsa curl jpeg ncurses png sasl sdl ssl threads vhost-net -bluetooth -brltty -debug -esd -fdt -hardened -pulseaudio -qemu-ifup (-rbd) -spice -vde -xen"

QEMU_SOFTMMU_TARGETS="x86_64 -arm -cris -i386 -m68k -microblaze -mips -mips64 -mips64el -mipsel -ppc -ppc64 -ppcemb -sh4 -sh4eb -sparc -sparc64" 
Defines the targets for the full system emulation. 
This mode allows you to emulate a complete machine and to install a different OS on another architecture. 

QEMU_USER_TARGETS="-alpha -arm -armeb -cris -i386 -m68k -microblaze -mips -mipsel -ppc -ppc64 -ppc64abi32 -sh4 -sh4eb -sparc -sparc32plus -sparc64 -x86_64" 5,217 kB      
Defines the targets for the user space emulation. 
This mode allows you, for instance to run a program compiled for Linux ARM in your Linux x86_64 environment.

So: did the necessary kernel configuration: 
	Virtualisation/KVM ; Processor.../Paravirtualisation-support ...
Rebooted to new kernel.

Emerged qemu-kvm with options as shown above.

Added "user" account to the kvm group, for access to /dev/kvm.
Loaded the kvm kernel-module, but still saw no /dev/kvm .

Made new disk-image (preallocation of metadata; auto-growth of data)
 $ qemu-img create -f qcow2 -o preallocation=metadata disk.image 40G
(took ~1s).

Tried running:
 $ qemu-kvm -m 768 -smp 1 -hda /space/vms/disk.image -cdrom /tmp/kubuntu-10.10-trinity-desktop-amd64.iso  -boot d

But that failed: no /dev/kvm 
Checked the web: possibly the virtualisation is disabled in BIOS, even 
though the CPU is thought (from the 'svm' found in 
    egrep '(vmx|svm)' --color=always /proc/cpuinfo
to be capable). 

Tried other qemu command:
 $ qemu-system-x86_64 -m 768 -smp 1 -hda /space/vms/disk.image -cdrom /tmp/kubuntu-10.10-trinity-desktop-amd64.iso  -boot d

It noted that there was no /dev/kvm, but it ran anyway, presumably switching to 
a less efficient emulation.