on ubuntu machine, follow these steps
0-download ubuntu 10.04 or other releases
lets call this file ubuntu-10.04-server-i386.iso
1- install kvm using
aptitude install kvm
2- create a disk image using dd. let say 5GB disk image
dd if=/dev/zero of=ubuntu-server.img bs=1G count=5
3-assuming that iso and ubuntu-server.img files are in the same directory.
create kvm vm using the following command. This vm will have 512 MB memory.
kvm -m 512 -cdrom ubuntu-10.04.iso -boot d ubuntu-server.img
to test it, run the vm using
kvm -m 512 -cdrom ./ubuntu-10.04-server-i386.iso ubuntu_server.img
done