Apple Admits Leopard BSOD Issue
According to the support document the issue may be related to "third-party 'enhancement' software installed that does not work with Mac OS X 10.5 Leopard." The document lists two different solutions.
Solution 1: Reinstall Leopard (recommended). It may be necessary to perform an Archive and Install installation of Leopard.
Solution 2: Use the command line (advanced) to remove application enhancement software. Try this solution if you are comfortable using Terminal and have certain application enhancement installed.
One issue is that some users are apparently seeing the BSOD without APE installed. This is likely not the end of this.