I just installed the latest version of Qemu on my Gentoo machine and I am impressed how easy the installation was. I am really impressed. I did not have to configure any interface or stuff, I just installed Qemu Version 0.9.1 and also KQemu (1.3.0 pre11) put in the CD of my Windows XP copy and ran these commands:
$ qemu-img create -f qcow2 /path/to/xp.cow 1300M
$ qemu -hda /path/to/xp.cow -boot d -cdrom /dev/cdrom -m 384 -localtime
and then to boot into my XP from my Gentoo:
$ qemu -hda /path/to/xp.cow -boot c -m 1000 -localtime -k de -usb -soundhw all
Man, Fabrice Bellard I am just a bit baffeled how easy and smooth this went. Thank you!
OMG: Sound works as well.
This is far more easy to install then VirtualBox for me. Vista does not work yet though at least not during my last try.
Vista-Qemu-Update:
Vista does not want to install. I get following error:
I googled and this seems to be an ACPI related error. Maybe my Bios does not fully support ACPI to the satisfaction of Windows Vista.
Update: There seems to be a solution for this problem, I just searched the qemu-mailinglist-archives.
Update 10.4.2008: Guess what, now it works quite smooth! Just installing Windows Vista on my Qemu-Gentoo.
Open Source Teddy Bears 
I am getting that exact same error running the latest version of Qemu. Any luck getting it working? I need to get vista installed for testing @ work (wouldn’t touch it with a stick if it wasn’t work).
Thanks
I just installed the latest GIT Version of Qemu a few days ago and I still get the same error. They may have fixed something in the mean time. But if you need a working Vista _now_ then I recommend you install VirtualBox. My Vista “Ultimate” works fine in VirtualBox.