This page has some guides for run KVM under Linux, specifically Ubuntu
Install the packages you need like so
sudo aptitude install qemu-kvm libvirt-bin ubuntu-vm-builder bridge-utils
I also find these other packages helpful
sudo aptitude install virt-manager virt-viewer virt-goodies
Libvirt is the method we're using to manage the VMs. It wants to put disk images in /var/lib/libvirt/images/ but I prefer /opt/vm/kvm so I just relink it.
sudo rmdir /var/lib/libvirt/images sudo mkdir -p /opt/vm/kvm sudo ln -s /opt/vm/kvm /var/lib/libvirt/images
Run this command
sudo adduser yourusername kvm
Now you can create a VM! run this command (it can also be found in the Gnome menu under System Tools => Virtual Machine Manager)
Click on File=>Add Connection and choose KVM/QEMU Localhost
Right-click on the localhost (QEMU) and choose New. This will bring up the VM creation wizard.