Apple has released an update to Java for people who are running OS X 10.5 Leopard. This appears to be a security fix, but in addition Apple has improved reliability, and compatability of Java in 10.5 with this update.
The update is for all Intel and PowerPC Macs running Leopard version 10.5.8 "or later" (indicating an upcoming release of 10.5.9?), and weighs in at 161.35MB. It is available through Software Update or from this Apple support webpage: http://support.apple.com/kb/DL924
The security content of this update should be available soon on this Apple knowledgebase document: http://support.apple.com/kb/HT3851