Yeh, Virtualbox is now released for AMD64 and it works!! We now have USB and Shared folders and Remote Display working natively
To get it to work do the following:
1) Install virtualbox-modules from portage to give you the vboxdrv module.
After you've installed virtualbox-modules you have to do the following so that you can get the usb working:
open up the file /etc/udev/rules.d/60-virtualbox.rules and change the line so that it reads "KERNEL=="vboxdrv", GROUP="vboxusers" MODE=666"
You also need to add your self to the "vboxusers" group via the kuser app.
2) You can download Virtualbox 1.4.0 from here:
http://www.virtualbox.org/download/1.4. ... _amd64.run
Turn it into an executable, open root
konsole to downloaded location and type
"./VirtualBox_1.4.0_Linux_amd64.run install /opt/Virtualbox
There is also the ebuild in portage but it seams to be broken at the moment for amd64 users.
Then reboot your computer and all should work.
There should be a shortcut in kmenu->system->virtual machine or just open up a command konsole and type "Virtualbox" (capital V)
If anyone gets stuck then I'll try to help.