The Web Ballistics computer was written to address these problems. It will work with any computer running a modern web browser. To use the Web Ballistics Computer, you must have a forms-capable browser. You'll know if your browser is forms-capable if it can display buttons and text fields.
The Web Ballistics computer can be found at:
http://weber.u.washington.edu/~basiji/Ballistics/wbcIntro.html