I think this is browser-dependable issue. If you're using IE, you should try to search some tutorials about browser's internal functions and objects from MSDN Library (http://msdn.microsoft.com/library).
Let's just hope somebody can help you further, because I've never heard it'd be possible to print without prompting. Though, IE has infinite number of features to use.
Edit:
Closed due to this thread (http://www.codingforums.com/showthread.php?s=&threadid=224).
No cross-posting allowed !
Read the RULES (http://www.codingforums.com/rules.htm) for more details.