for a lucid explanation of what's going on
with Wubi. It's an ingenious way to provide yet one more
option for Windows users to try Linux, between Live CD
which may be too sluggish to show what Ubuntu can really
do and a full dual-boot installation in a separate
partition which may seem fearsome to starters.

But this has triggered another question I would like to
have answered at some point. Not that I don't do my
homework; I really spend a lot of time studying man
pages and documentation on line. But the following has
never been made clear:

I have dual boot, my original XP on hd0,0 and Ubuntu
on a separate drive hd1,5. The grub loader configuration
file menu.lst is obviously on hd1,5 but I wonder if it
is called from the MBR on hd0 which Windows recognizes
as C: and which is set in the BIOS as the primary drive.

Is this right? If so, how is it that Linux got Windows
to relinquish the first reading of this MBR upon
the Ubuntu installation? If I choose Windows from grub
then I assume it simply returns control of the MBR
back to Windows as in the original case?

What, exactly, changed on hd0,0 when I installed Linux
on hd1,5? Certainly nothing in the XP operating system
itself, right? only the MBR?