Difference between XP and Vista/7?

[Shao Sean]

Basically you cannot modify anything in the "Program Files" directory  
(or any sub-directories)..

Vista does something called "virtualization" where it makes a fake  
copy of the "Program Files" for the use of your application when it is  
run.. It does this to trick your program into thinking it can still do  
the old XP thing of modifying the "Program Files" directory, sadly  
these changes are only temporary (once your program quits the changes  
are gone)..

The best thing to do is to check the systemVersion and to use the  
AppData folder for Vista and greater.. You should also be doing this  
on Mac OS X (Application Data or Preference) as well as Linux..  
Basically think like this "My program is set in stone in the  
application/program files directory"