At my aunt's request, I've been working to set up a dual boot situation on her laptop. It previously had Vista installed, and I had an XP disk/key that I wasn't using on my systems.
Aside from various relatively normal kinks along the way, things seemed to be going along fine. After a few boots between Vista and XP (I had to reboot XP multiple times for updates, and Vista once to check a few settings for a critical application), the system stopped booting (the boot process failed before the multiboot menu, so neither OS could be booted). I've tried a number of fixes that I already knew of or researched, including Rescatux's automated tool for fixing Windows MBRs as well as executing "bootcfg /rebuild" from the recovery console reachable through the XP install disk. I also tried repairing the XP install and then tried completely reinstalling XP. Even that didn't leave the machine in a bootable state, which has me extremely concerned.
The most frequent error message is displayed below; this is the one that displays after starting an install of XP from the CD.
Invalid BOOT.INI file
Booting from C:\windows\
Windows could not start because the following file is missing
Please re-install a copy of the above file.
Some attempts to use Rescatux to recover the MBR have resulted in different booting behavior (essentially, a short, non-informative output consisting of "MBR" followed by 1-2 numbers and a colon, followed by a system freeze). I don't recall any other booting behavior, though it's possible that other booting behavior has been exhibited but forgotten.
I *haven't* yet tried running "fixmbr" from the Recovery Console to completion; the tool complains about "a non-standard or invalid master boot record", and warns about the risk of losing partition data. Though I do have a backup of the user data from the Vista system (and am still able to back up any needed data by mounting the drives in Linux), I'd rather not try that unless I'm certain the partitions wouldn't be lost.
The partition table of the hard drive originally contained a small partition at the beginning, which I have left unmodified. The remaining disk space used to be entirely devoted to Vista, but now only half of that space is dedicated to Vista. According to GParted, a clean install of XP on the unallocated second half of the drive creates an *extended* partition, which in turn contains an NTFS partition. If a Linux system instead creates the NTFS partition, and the XP CD is simply told to use that partition as is, then GParted shows an NTFS partition after the XP install as expected, but boot behavior isn't affected by this (the system still fails to boot). I imagine that this could be at least part of the problem since (to my awareness) XP installs are only supposed to exist on primary partitions.
The tools available to me to fix this problem are an XP Professional CD and key as well as a flash drive dedicated to YUMI (in essence, I can use it to boot almost anything available as a LiveCD, including Linux distros and recovery tools). Notably, I *don't* have a Vista CD; my aunt is here on travel, and unlike my XP disk, I don't have an extra copy of Vista available.
In the absolute worst case scenario, I can maintain backed up data, wipe the entire hard drive, and install XP on the entire system. In an effort to avoid using such drastic measures without warrant, I was hoping that somebody else might have a few ideas on diagnostic methods or anything else that I may have overlooked while working on this.