I am trying to find the correct XP Home Edition Retail or OEM?). Which
one I should get?
I strongly recommend the Retail Upgrade, not the Retail Full, and not
the OEM version. Although if you get a complete generic OEM version,
it contains the same software, its license ties it permanently to the
first computer it's installed on. It can never legally be moved to
another computer, sold, or given away (except with the original
computer). That means that if the computer dies, your Windows license
dies too.
The reason I recommend the Retail Upgrade over the Full is that it's
much cheaper and the requirement to use an upgrade version is to *own*
a previous qualifying version's installation CD, not to have it
installed. When setup doesn't find a previous qualifying version
installed, it will prompt you to insert its CD as proof of ownership.
Just insert the previous version's CD, and follow the prompts.
Everything proceeds quite normally and quite legitimately.
Most people already own a previous qualifying version, but worst case
if you don't, you can inexpensively buy a copy of Windows 98 someplace
like eBay.
I want to update XP Home to SP3 too. Or XP
Professional is ok, but I can't find a good deal or place to buy XP
Home or Pro.
Professional costs considerably more than Home, and unless you need to
join a domain (except for those people in large corporations or
universities, most people don't), Home is just as good for almost
everyone.
Where to buy it? A google search will turn up many sources, for
example, Amazon.com.