"Press any key to boot from CD.....Error loading operating system"

My name's Jonathan, this afternoon I reinstalled Vista, and tonight have made an attempt to install XP in a dual boot format. As you may have figured, the above message is what I get on the reboot. My current layout of drives is:

C: | System - Vista | 20001MB
D: | Essentials | 39998MB
E: | System - XP | 20002MB
F: | Storage | 225231MB

Would the bootloader still be Vista's? Or XP's? Would the bootloader be the problem to begin with? What fixes can I implement given that I am unable to boot into any operating system at all on said PC? Any other ideas?

I have both an OEM XP and Vista CD (perfectly legal mind you) if that's of any help to you at all.