Hi, i am fixing a computer for a friend and am trying to install xp on a hd that was running ubuntu. When i get to running windows on the instilation screen, it freezes.I am told this is because of the MBR. How do i fix this?

Actually, the situation that you describe is a little different. You are installing Windows on a system that currently has the whole hard drive formatted with a Linux partition, correct?

If you have you Ubuntu disk handy, you can fix this. Windows is unable to read Linux partitions, so it hangs during the installation, as it is unable to find a valid Windows partition on the hard drive.

See this Microsoft article.

You can also use any Modern/ recent good Linux live CD to fix the problem as well. You need to partition the drive as a fat32 partition, so the Windows installer can see the drive correctly.

Also, if the computer is a very new one (less than two years old), then realize that Windows XP does not often see sata drives correctly, without drivers for the chipset handy during the installation.