Windows 2002 refers to the server versions that will come out next year. They were planning on naming it Windows 2002 but it looks like they are going to use one of their .net monikers instead.
Windows XP Home Edition
Windows XP Professional Edition
Windows XP 64-Bit Edition (for Itanium processors)
There will be the usual different versions of each, full version, upgrade, Select (for corporate users that have a MS Select deal in place), MSDN, etc. The only difference between these are the licensing and activation piece and the install piece for the upgrade versions (they make you prove you own a qualified previous Windows version).