This is a tough situation. If the Server2003 was in the first partition, then you have probably deleted the active boot partition and the Windows bootloader although I think the MBR is still there. At boot time the MBR is trying to pass control to a bootloader but can't find one now, and so you get the error message about "DISK BOOT FAILURE".

What to do next......it depends. After deleting the Server2003 partition, what were you planning to do with the free space?