Pre-orders and previews begin April 10, launches April 24.
Mac OS X Leopard on October 26th?
They specifically point to October 26th as the likely ship date for Mac OS X Leopard, but don't rule out the possibility of additional announcements near that date.
ThinkSecret also believes that Leopard will launch on or around October 26th.
Mac OS X 10.5 Leopard is available for pre-order at Amazon