Somewhere in here, someone suggested the following install method, which worked for me:

*reboot into Single User Mode (hold down CMD-S immediately after you hear the restart chime until you see the spinning gear)
*use Applejack if you have it installed or use the fsck command shown when the prompt becomes available
*when it's done, type reboot at the command prompt
*when you hear the chime, hold down the SHIFT key until you see the spinning gear
*Repair permissions with Disk Utility (Applications>Utilities>Disk Utility)
*Install Application Enhancer
*Install Windowhade X
*Restart the computer
*Repair permissions again.

This method worked for me.
Mac Pro (early 2008-3rd generation), 10.5.4