When I was setting up a dual boot I was getting the "/ntldr not found or corrupt error".
Doing some research I read that the files could be copied from a known working system. So, I copied the ntldr file from a working XP machine to the machine that I was getting the error.
Attempting the boot after this I didn't get the ntldr error but a different one that related to the HAL (Hardware Abstraction Layer) dll. (I think that it was "hal.dll not found" - but I was getting a little out of my depth by this time!)
So, I decided to retrace my steps. I could boot WindowsXP after I had performed the XP install but I could not boot into Vista. I knew it was still there as it was still showing on the C: drive. XP was installed on the D: drive and as I say the computer booted just after I installed XP. So it would seem that ALL the bootloader files and the bootloader itself were working as they should.
However, the bootloader for XP is not the same as the one for Vista and as William pointed out in his tutorial you need to fix-up the Vista bootloader so that the computer will boot into Vista and hopefully (optionally XP) using the bootloader menu.
The fix was to use the Vista install DVD, except that instead of doing an install you chose the "Repair your computer" option. This hopefully restores what the XP install did to the Vista boot. It didn't work for me!
I had a backup image of Vista so in the worst case I could re-install that from scratch. I thought I would try a few more things first.
I re-installed XP again so that I could boot into XP again - whatever I did to the Vista install and the bootloader I am not sure. I tried to edit the boot.ini file using the bcdedit.exe utility which you can access when you boot from the Vista install DVD. I was not successful!
Doing some more research I came accross a utility called VistaBoot Pro. This was supposed to sort out all bootloader problems and configure your boot.ini file as it should. I think they say bcdedit made simple.
This utility runs in XP and you can edit the boot.ini file (I am not sure if it is the same file for XP and Vista but I think that it is). To cut a long story short - after installing Vistaboot Pro and running it to fix up my bootloaders I was able to boot into XP and Vista. I think that there was an option to load the "Legacy Bootloader" - to be honest I am not quite sure what I did but it fixed the problem.
Full circle ---- I am not saying that Vistaboot Pro is what RedW needs to fix his XP only problem, but Squirrelnmoose is probably correct that the system files are not being found when the system boots - not that they are missing or corrupt. The message is generic.
You also get the same "Repair your computer" on the XP install CD. However, this does not help RedW as he can't boot from the CD! What I think happens when you run this is that the "repair" fixes up the bootloader (appropriate for your system) and makes entries in boot.ini so that the bootloader knows where to find things.
There is a very detailed explaination here: BOOT.INI file for Win2000/XP/2003
Red's case should be a lot simpler that this as all he wants to do is a single boot! However, there is a lot of information in the link above that might give some hints on what to edit. There is also a utility called bootcfg.exe (see the MS page How to edit the Boot.ini file in Windows XP
- but it is only available in XP Pro (not Home).
Hope this helps