Dual monitor crash on PB667

[Wayne Swingle]

I am experiencing system lockups since upgrading to OS 10.25 and 10.26 
on PB 667, when using an external display as well as the built-in LCD.  
When resizing, moving, or minimizing a window on the external VGA 
monitor, the system will completely freeze forcing a hard restart. Any 
insight? Are the graphics enhancements in quartz extreme overtaxing the 
built-in 16 meg Radeon Mobility?