The boot files for XP, i.e. boot.ini, ntldr, and ntdetect.com,
are left in place in the XP System partition (the partition that
contains the boot files - which is frequently to same partition
that contains the operating system, the "Boot" partition). The
Vista boot manager is told in the BCD to just pass control to
those same files in the same place as they used to be. They
are not moved, not re-created, nor in any way diddled with.
Vista just leaves the past to work as it always did. The
indication in Vista of the presence of old Windows installations
is in the BCD, and the command line utility "bcdedit" can be
used to remove those references if that is what you want.
*TimDaniels*