For a free, Excel based Ballistic Computer used by several members of the Long-Range Hunting forum, go to:
Choose the Ballistics Link and you will find two Ballistic Computers for download. They are both based on the same program but are set up for different uses. The RBC (Ranging Ballitic Computer) can calculate ranges from MIL Dot or GPS data and dislpay the correct corrections.
This system was developed by Dave King and Peter Cronhelm (thats me) and it has been used for shots beyond 1 mile.