Apple released their latest update for Mac OS X 10.5 Leopard. The 10.5.7 update includes security fixes and reliability improvements. You can install it using Apple Software Update or downloading it directly from Apple (10.5.7 Update or Combo Update).
As for Mac OS X 10.4 Tiger, Apple released the Security Update 2009-002 which includes updates “addressing potential security flaws in Apache, ATS, BIND, CoreGraphics, Cscope, CUPS, disk images, enscript, Flash Player, Help Viewer, IPSec, and more. In many cases, the flaws could allow someone to crash applications or run arbitrary code when users visit maliciously crafted Web sites or open maliciously crafted PDF or Flash files”. It is available as a stand alone download for PowerPC and Intel based Macs.