Yes, ALL of Microsoft products eventually reach what is known as an End of Life (EOL) state where they are no longer maintained in any way, except for special patches generally available only to very large clients.
I think, but someone else can probably confirm, that this will happen for XP sometime in 2012. There's a page on Microsoft's site, if you can manage to find it, that gives specific time frames for this.
Does anyone know whether Windows XP will be discontinued and not updated any more by Microsoft? Thank you.