First of all, the .ova format is nothing more than a tar archive, containing an .ovf and a .vmdk files, respectively the VM configuration and disk.
So, you can simply extract the files:
$ tar xvf MyAppliance.ova
And convert to a format appropriate for qemu/kvm:
# List the available formats $ qemu-img -h | tail -n1 Supported formats: vvfat vpc vmdk vdi sheepdog raw host_cdrom host_floppy host_device file qed qcow2 qcow parallels nbd dmg tftp ftps ftp https http cow cloop bochs blkverify blkdebug # Do the actual conversion (I chose qcow2 here) $ qemu-img convert -O qcow2 MyAppliance-disk1.vmdk MyAppliance.qcow2
Have a look at the .ovf too, for information on expected machine configuration / resources (eg. memory and cpu).
After the conversion, simply create a new VM and make it use the newly created disk as the primary harddisk.
I had some issues converting the image using the qemu-utils version 0.12.5 shipped with debian squeeze/stable (the resulting image was just some megs of garbage); I had to upgrade it to version 1.1.2 from wheezy/testing, which worked just fine.