As expected, thousands and thousands of eager Mac users rushed out to buy and install the new version of Mac OS X, Leopard, over the weekend. And for some it did not go well.

The most common Leopard install problem, in all its cruel irony, is a Windows-like Blue Screen of Death as the Mac nears the end of the install process. Affected users report a system hang with a blank blue screen. Ugh.

The finger of blame has pointed mainly to third-party software from Unsanity, specifically its Application Enhancer system hack that enables several of the company’s utilities to alter parts of the Mac operating system (they’re actually called “haxies”). As a long-time fan of Unsanity’s FruitMenu, which creates a fully customizable Apple Menu, I have had APE installed on my Macs for years. It’s unfortunate, if not surprising, that such software would create problems with a new version of the Mac OS.

Unsanity says the problem could be caused by incarnations of APE earlier than version 2.0 that users still may be running on PowerPC-based Macs. Previous versions of APE won’t run on Intel-based Macs, so these newer Macs appear to be immune to the problem.

Some affected Mac users who found a way to delete the APE components were able to install Leopard successfully. An easier option for less technically adventurous users afflicted with the dreaded blue screen is to reboot the Mac with the Leopard DVD and re-install using the “Archive and Install” option (instead of the default “Upgrade” option). This should remove the offending components and allow Leopard to install properly.

To make matters worse, some users have reported unusually long install times apart from the APE issue. Apparently the installer does a full hardware check before rebooting the system. Some who called Apple’s support line said they were told this process could take up to three hours. Because the APE issue causes a permanent hang at the same point in the installation, many users can’t be sure how long to wait before giving up and attempting a re-install.

My advice: Use “Archive and Install” and be patient, no matter how much the wait kills you.