Isn't there a way to hide partitions from each other in GRUB?

I have Vista(OEM) and XP(?) on a mega-boot machine F10/Ubuntu/PCLOS/Vista/XP. I booted XP today, and since I'm missing a driver in XP, I booted Vista. Except XP booted again. And again and again...

I can restore the Vista loader, but it's gonna' be a pain. How do we prevent this from happening again? And why did this even happen? It's been multi-boot for 2 years (and multi-Windows too)???

Thanks

Are you sure that grub is even starting the Vista loader? Or has the grub /boot/grub/menu.lst changed?

If it is starting Vista and Vista is in turn starting the XP, then it is not really a grub issue; grub merely chains to the Vista loader (it cannot hide what is visible through the BIOS). You could perhaps 'conceal' the XP partition by mapping it to another drive in the menu.lst entry for Vista (I have not tried this). But even if you succeed in stopping Vista seeing it, you may still have to deal with the reason why the Vista loader is not working.