The guidelines of pressing F10 are needed if in BIOS your DVD drive is not first boot device, but still safe and better to use this method. If you select CD/DVD device from boot menu and still get BootMGR is missing then you are not booting from CD/DVD drive but from hard disk. The possible reasons are
- CD you have got is non-bootable
- CD you have is damaged
- Your DVD drive does not support booting from CD (which is highly improbable)
- You are not selected the correct DVD drive to boot from after pressing F10
We can rule out the last 2 possibilities and the left ones are that CD is somehow messed up. Check if you can use the same CD to boot from on another computer.
You can borrow a Vista install DVD from a friend. Or create a Vista recovery CD from a friend's computer. Or you can download ISO image
from internet. Then boot from this CD/DVD, and follow startup recovery options as detailed here