MOre basic VB questions - Text Box control

[JEngh]

Thanks to the VB GURUs for help on my previous text box question. Here is another one for ya! Say I have three text boxes that I input info into: A, B, and C. Say I also have three text boxes: 1, 2, and 3 that the info. I put in the first three goes into them as follows:
Input from A goes to 1
Input from B goes to 2
Input from C goes to 3

For the purposes of boxes B and 2, I am not doing anything, but taking input from B and putting it in 2. That works fine. My problems are with A and C and 1 and 3. The best way to illustrate is with an example:

Part A: input works
Every time I input new values for boxes A, B, and C, this new input should be generated on a new line in boxes 1, 2, and 3 as follows:

Text Boxes Text Boxes
A B C 1 2 3

input from me: 1 3 5 fills boxes: 1 3 5
input from me: 5 7 8 fills boxes: 5 7 8
input from me: 9 14 96 fills boxes 9 14 96

Part B: input problem
If a new line of input to A and C is like below (value in A matches what is in 1 but the value in C does not match what is in 3) or (value in C matches what is in 3 but the value in A does not match what is in 1), the followng below should happen:

Text Boxes Text Boxes
A B C 1 2 3

input from me: 1 3 5 fills boxes: 1 3 5
input from me: 5 7 8 fills boxes: 5 7 8
input from me: 4 7 8 Should produce error message
input from me: 5 7 12 Should produce error message

The first message should read: "Duplicate entry, the value of A <and it should pull out the value 5> exists on 8."

The second message should read: "Duplicate entry, the value of C <and it should pull out the value 8> exists on 5."

In both instances, these values are coming from boxes 1 and 3 which are what are getting filled by input from boxes A and C respectively.

I am using regular text boxes. Please help if you can.