all those with this error message...
C:\Windows\system32>bcdedit -set {ntldr} device partition=C:
An error occurred while attempting to reference the specified entry.
The system cannot find the file specified.

you should just install easybcd and add entry of windows xp, name it and give it the drive letter of where the xp is installed.but if the drive letter is grayed out, give the drive letter first before u select os and name it.
if u have the error message booting into windows with the ntldr and 0x0000etc error message do the same thing with easybcd and u are done.use easybcd in vista.
it worked perfectly for me.now i can boot with ease.no problems.
thanks mr william.