Apple on Monday released for download a significant update to its Leopard operating system for Mac computers.

OS X 10.5.6 includes at least three dozen fixes for issues ranging from print reliability to archiving problems. The update also offers "general operating system fixes that enhance the stability, compatibility, and security of your Mac," according to Apple.

Apple cautioned users to proceed cautiously with the update. "You may experience unexpected results if you have third-party system software modifications installed, or if you have modified the operating system through other means," Apple said in a note on its Web site.

Users could also have trouble "if you have moved applications from their default locations," Apple said.

For those wishing to press ahead, the free download for existing Leopard users offers a wealth of performance, convenience, and security updates.

IChat users will see fixes for an issue that causes an encryption alert to appear in the chat window and for a glitch where users who set their status to "invisible" are automatically logged out of iChat.

For gamers, the update includes modifications that will improve performance of a number of games and fix image distortions that occur with some ATI graphics cards.

Mail users will see a fix for a problem that causes messages identified as junk to remain in the in-box, while Mobile Me fans will enjoy faster syncing for contacts, calendars, and bookmark lists. Graphics pros will get improved performance with Adobe's C3 application suite.

Mac OS X 10.5.6 is, among other things, also designed to improve performance and fix bugs in Apple's Time Machine archiving system, Safari Web browser, DVD player, and TrackPad portable input system.

Apple on its Web site has published a full list of the issues that the update is designed to address.

Apple debuted OS X 10.5, or Leopard, last year. Its slick interface and business-friendly features have helped Apple make inroads against Microsoft Windows in consumer and business computing markets.