Need an XServe without paying Apple for the privilege? Psystar has something for you. They’re releasing 1U and 2U servers running Windows, Ubuntu, and “even Mac OS X Leopard Server.”
Again, these boys are risking a lot selling these things, but more power to them. These are OEM rack servers with a little Psystar work and not much else, but it starts at about $2,000 and OS X costs a little extra ($500-$1,000 for OS X Server). Get them while you still can.