First check if you have Java Web Start.
You can do this by searching (use the Start menu to search) for the file
If you do not have Java Web Start you need to download it.
If you have Java Web Start you can start the calculator just by clicking this link:
Warning: when you launch for the first time you will getting a message warning you that I don't have a valid certificate (they cost a $100 or so) and asking if you still want to start the program. Ignore this warning. The first time you Launch will be slow since many files may have to be downloaded but after that it will be fast.
After the first time: You can start the program either from this web page or just by executing javaws.