Encryption program writing

Hi, Ive written encryption programs before, but I need help, cos Ive got a great idea on a method of encryption, but I have no idea where to start, the idea involves two arrays where the letters that make up the message are mixed in with random letters and numbers, and then the entire array is written to file, but at the same time, a second array is written to a different file that has the location of all the message characters that are in the first array. This encryption idea could then be made more compilcated by having multidimentional arrays, thats the plan, so, any tips, ideas on where to start??? :D

* read the message
* create an array with all the alphabets and symbols you use
* randomly equate the message alphabets to aplhabets in the array
* store the "encrypted" message in a text file
* store the array whichs tell you what the alphabet actually means in a different file

I think you should have a look at simple encryption algorithmns such as columnar shift, vigenere etc which are more secure than your method.. for example vigenere uses a key.. so you dont need to save the "index".. instead your message can be encryped and decrypted based on the key(read password)...

As a side note, if you really want to get into cryptography, a very good and accessible book is Modern Cryptography: Theory and Practice by Wenbo Mao.

You might want to take a look at some of the websites listed from dmoz's cryptography subdirectory