Joe said:
Full version of Home Edition with SP2 is about $180-$200, with
Professional running around $100 more than that.
If you have a qualifying product (such as Windows 98) already, then
you can get a Home Edition upgrade for about $100 or Professional
Edition upgrade for about $200.
And even if you don't already own a qualifying version, you can usually buy
a used copy of Windows 98 very cheaply. Since that's a legitimate way to
qualify for the upgrade version, and since the combination of Windows 98 and
an Upgrade version of XP will almost certainly cost much less than a Full
version, it hardly ever makes any economic sense to buy a Full version.
One additional point: OEM versions are also widely available at low prices,
and some people confuse them with the Full version. I almost recommend
against buying an OEM version, since it comes with several restrictions, the
most severe of which is that once installed on one computer, it can never be
legitimately installed on another.