A Bootmgr missing is an error that involves Vista and up so I am assuming the drive with the Bootmgr missing error still has a OS on it. XP uses Boot.ini and ntldr. Do you have a XP or Windows 7 install disk?
I would do the following. Put in the disk that gives you the Bootmgr missing error. You can use a Gparted live CD as suggested by TheGreatGarbled or you can download the bootable version of Partition Wizard which is a smaller download and a little easier to work with. Download the iso file and burn it to a CD by double clicking the file in Windows 7 or by using Imgburn if using XP. Just watch out for the optional program installs. After booting Partition Wizard, wipe the disk using the Quick Method. After wiping the disk, you create a new partition and format it NTFS or let the install disks of XP or Windows 7 do the format and partition for you at install.
I believe you are getting the error because you have the hard drive as the first boot device in BIOS. You will have to change the first boot device CD/DVD.
If you have problems booting to CD/DVD it may be possible to boot to a USB flash drive if the computer has that option.
How much ram is on the computer. You may not be able to run Window 7 on it. Linux may be the best option. I will have to look at the specs to see which distro would be best.
Edit: It looks like this computer could run Windows 7 without a problem. Do you know the size of the hard drive with the Bootmgr error?
Edited by JohnC_21, 25 June 2014 - 04:56 PM.