CYPHER Idea

Hello,

I am trying to develop a web-based encrypting/decoding application. I have created a GUI where a user can input a message, then they input CODEWORD in another window. Then they press encrypt button. This converts characters in message into another character, ie A=01, B=02, C=03, and so on. How do I convert the character in the message into another character? I am not a programmer yet. Most of my experience is with designing. Has anyone seen similar programming?
Once the message is encrypted the new message is copy and pasted into email and sent to recipient. They paste the encrypted message into window, type in codeword and press decode button, which converts characters back into original format.

The idea is to have 4 codewords to choose from. Each code has its own encryption. IE Code1: A=01, B=02, C=03…Code2: A=26, B=25, C=24…Code3: A=0Z, B=0Y, C=0X… Get the idea? I am assuming the characters have to assigned in the AS. The =characters are what gets displayed in the encrypted message.

Thank you.
http://sergemedia.net/cypher/cypher.html
Here is the GUI.