If your friend installed Ubuntu to the partition your Windows install was on, then there is no recovering your data, your friend just overwrote it.
If he installed it as a live cd then you should be able to just mount the drive, see the files, and then copy them to a different hard drive or flash drive. http://www.psychocats.net/ubuntu/mountwindowsfstab
If your friend installed Ubuntu to the partition your Windows install was on, then there is no recovering your data, your friend just overwrote it.
If he installed it as a live cd then you should be able to just mount the drive, see the files, and then copy them to a different hard drive or flash drive. http://www.psychocats.net/ubuntu/mountwindowsfstab