On my laptop I've got Vista and XP installed and they're working fine in a dual-boot configuration. I installed XP first and then Vista.

On my desktop at home I installed Vista RC2 and then, for app compatibility reasons, I went off to install XP Service Pack 2 because some of my software doesn't run on Vista RC2.

Problem is - part way through the installation of XP I came across the problem logged in this KB article;

Windows Vista no longer starts after you install an earlier version of the Windows operating system in a dual-boot configuration

When I found the KB I was pretty pleased because at least there's a workaround that seems pretty simple but I've yet to get this to work for me.

I went through the;

Drive:\boot\ Bootsect.exe –NT60 All

and that seemed to work but when I get to the bits involving bcdedit.exe I seem to find that no matter what I do bcdedit reports;

device unknown

no matter how many times I do "bcdedit.exe /set {bootmgr} device partition=C:" I always end up with "device unknown" and the PC won't boot.

Now, I've a sneaking suspicion that this is something to do with my volumes being dynamic volumes but that might be a red herring.

I'll update the post if I find an answer but, right now, I guess I'm going to be in to reinstalling XP and reinstalling Vista and, at this late stage in the game, I might try and wait for Vista to RTM before I install it again.

Update 1 (the next day...)

I finally got this sorted out but, unfortunately, it's one of those where I'm not exactly sure how I fixed it. First off, I installed a second version of Vista onto the same machine on another partition, booted into that and attempted to fix the first installation from the second but I'm not entirely convinced that it's this that fixed it for me.

I still see that when I do a bcdedit.exe I have "unknown" entries for device and osdevice so clearly that was a red-herring and not what was causing my problem.

I think that what possibly fixed it for me was me finding the backup files in c:\boot named bcd.backup.0001 and upwards and I tried doing a bcdedit /import on the first of those files and it seemed to help.

I've not yet been brave enough to try and get XP onto this machine again but here's my best advice if you're doing this - make sure that you do;

bcdedit.exe /export "path to some file"

and save off your existing working boot configuration before you attempt to install XP after Vista - at least that'll give you a known state that you can return back to if things go wrong.

I'll try this again myself at some later point and will update the post again afterwards.

Update 2 (the day after the next day...)

I had another go at making this work. I followed my own advice in that I backed up the BCD database using the command above. I then went and installed XP onto a different partition (and disk as it happens) and, as expected, it broke my Vista boot manager.

I then went and restored the BCD database (my "ace in the hole") and, guess what, I still couldn't get the PC to boot :-(

I'm pretty embarrassed at how much time I've spent trying to get this to work - I reckon I've spent about 10+ hours on it and it's been a fruitless 10 hours. I find that debugging this new boot manager system isn't easy (it perhaps is if you know more about it) as it's a constant trial and error of rebooting the PC and then seeing if what you just changed fixed anything.

In the end I did the following to get to where I wanted to be;

1. Unplugged all but one hard drive inside my machine.
2. Installed XP onto that one hard drive.
3. Plugged my hard drives back in.
4. Used the bcdedit.exe to tell Vista about the new XP installation I'd just made on another disk.

And that works fine.

I'm sure there's a better way of doing this as this is a pretty brute-force way of going about things but, in the end, it worked and life was getting too short for experiments to find another way. I did attempt to use the Repair tool that's part of the recovery options on the Vista installation DVD but, whilst that kept saying that I had a problem and kept trying to fix it, I couldn't get it to make the machine boot.