From http://en.wikipedia.org/wiki/Stack_overflow
  In software, a stack overflow occurs
  when too much memory is used on the
  call stack. The call stack contains a
  limited amount of memory, often
  determined at the start of the
  program. The size of the call stack
  depends on many factors, including the
  programming language, machine
  architecture, multi-threading, and
  amount of available memory. When too
  much memory is used on the call stack
  the stack is said to overflow,
  typically resulting in a program
  crash. This class of software bug is
  usually caused by one of two types of
  programming errors.
  
  
  - Infinite recursion
 
  - Very large stack variables
 
  
When this error is thrown, recursion is the more popular reason.  
I've tried the site in IE8 without problems, so perhaps it is an old version of IE causing a problem.