Another poster already responded to this, but I think the response was
misleading. I don't know that Microsoft has officially announced the upgrade
paths, but I believe that they will be:
XP (including the upgrade version) will qualify for you to install Windows 7
using an upgrade license. However, you won't be able to install Win7 as an
actual upgrade over XP (keeping your installed programs, etc.). You'd have
to do a clean installation of it. None of your programs or settings would be
preserved. (The *data* on the drive would not be destroyed, though.) All
that you'll need to buy, though, is an upgrade version.
You will be able to use an upgrade license with your laptop. You could
install Win7 over Vista as an upgrade. (There may be version restrictions
that would require a clean installation, but the laptop should qualify for
an upgrade license.)
In my opinion, a clean installation of Windows 7 is safest. I tried the beta
(build 7000) of Win7. The first time I tried to install it was as an upgrade
over Vista X64. It was a bit of a mess; for example, most of the help files
for Win7 didn't install. A clean re-install was much better.
I don't know if the basic function of a Win7 upgrade license will be similar
to that of a Vista upgrade, but if it is, it's much less usable than the XP
upgrade. An XP upgrade license was essentially as functional as a full
license. (All that was needed over the full license was letting it find
"qualifying media".) A Vista installation using an upgrade license must be
started from a running qualifying OS; it can't be started directly from the
DVD. (It's slightly different in installing Vista X64 with an upgrade
license on a system with a qualifying 32 bit OS; the 32 bit OS can't launch
the 64 bit installation.) In retrospect, I wish that I'd paid the additional
$100US for a full version. It's hard to place a dollar value on annoyance,
but I've probably been through more than $100 worth with that damnable
upgrade license.
I wonder if Win7 will have the same feature as Vista, that is, the
possibility of performing an installation on a bare hard drive using an
upgrade license. (The procedure was: install Vista on the drive without
using a license key. That gives a 30 day demo version. That can be used to
launch the upgrade. In other words, you get a full installation using an
upgrade license, at the price of having to install Vista *twice*.)