This announcement was found on an Engadget post, but originally blogged on the Windows Vista Team Blog.
Apple computer should follow this quickly with an inexpensive upgrade path to Leopard, which is due out this Spring.
Not having been a Mac user for long now I don't know how well Apple handles the upgrade paths, but with upcoming upgrades to both Windows and Mac OS's both should offer solid, easy, inexpensive paths for upgrading to these new versions.