The boot manager I was going to try is GAG.
It allows you to boot to OSs on second, third hard drives and will hide all other primary partitions (so your Win7 won't see XP, etc), but extended partitions stay visible. That way, you can have a D: drive that does show up in both for file sharing between OSs. But that could allow viruses to spread between the two.
I know changing gears completely may not be very appealing. But the directions for GAG were short and sweet and it might not take that long to try it out.
As far as your drive letters changing. . . that could be the problem. I know with NT (and it looks like Win7), the boot.ini had disk info in it as to how the OS would load. And if a drive letter changes, and/or some other stuff (been too long), it will keep the OS from loading. So, this might be a clue. . . You'd have to read up on the purpose of the boot.ini (which XP doesn't seem to use) and stuff like that. However, when you said it changed the drive letter, that set off alarms for me.
Dual boot question.
I download GAG yesterday and it wouldn't install. The install screen kept popping up and disappearing right away. I choose the windows XP install option even though I was in 7 and that opened up but told me it was not compatible with my system. Didn't go farther than that because I was getting frustrated.
Did you create the boot CD, or did you find another way to install it?
What I read is that you burn an ISO file to a CD, boot from it, and then run GAG from there. It loads itself onto the first sector of your hard drive and then finds partitions, etc. You pick the OS installs, name them, give them an icon, select "Hide partitions" and that was pretty much it.
So to me, it sounds like you plug in hard drive one, load the OS. Plug in HD 2, and load the other OS. Plug both drives in, boot with the GAG cd, find the OSs, etc. And then life is good. But, having never tried it. . .
Anyway, if you were in XP or Win7 and executing stuff, you might have been doing it wrong. And that's why the install would start and exit right away. It's not suppose to run from the OS. Unless you have a different version than I'm finding.
What I read is that you burn an ISO file to a CD, boot from it, and then run GAG from there. It loads itself onto the first sector of your hard drive and then finds partitions, etc. You pick the OS installs, name them, give them an icon, select "Hide partitions" and that was pretty much it.
So to me, it sounds like you plug in hard drive one, load the OS. Plug in HD 2, and load the other OS. Plug both drives in, boot with the GAG cd, find the OSs, etc. And then life is good. But, having never tried it. . .
Anyway, if you were in XP or Win7 and executing stuff, you might have been doing it wrong. And that's why the install would start and exit right away. It's not suppose to run from the OS. Unless you have a different version than I'm finding.