Had similar issues last night trying to install Vista on my PC. Got different errors each time, and after about 10-20 attempts the HDD got too hot and wasn't recognised by Vista to install onto (but BIOS picked it up). Swapped HDD's and after the 3rd attempt succeeded.
However, if the OS isn't loading, then hasn't the MBR gone wobbly? Have you tried clearing the CMOS? Although usually a fresh install should work...Do you have XP installed on another partition?