Windows XP will no longer be available from any legitimate source after June 30, 2008. You may be able to find old retail boxes on auction sites, but the price will probably represent its value and/or you risk getting something other than a safe, licensable, functional operating system.
Every new computer new PC for at least the next 2 years will come with Windows Vista, Linux, or some spotted GUI on a custom Unix kernel (Leopard). -- Scary thought.
It won't do any good, but make your feelings known. Sign the petition to Save WinXP at
http://SaveXP.com.