A/V Guys: How to Read/Change IR Codes?
 

I've got these two remote controls (TiVo and TV set) and use the TiVo remote 99% of the time. However, I must use the TV set remote every once in a while to change video mode (Normal->Full->Wide->Wide Zoom) by pressing the "Video/Mode" button on the TV remote. Kind of a pain, as the TiVo remote otherwise does everything, and the TV remote is otherwise useless.

Now on the TiVo remote is a button labeled "Window." Officially, this button is not used, and if you press it, nothing happens except TiVo confirms with a yellow LED that you did indeed just send some IR code.

My idea is to to install and configure an IR receiver & emitter that will:
(1) Receive the IR code from the TiVo remote when I press the "Window" button
(2) Convert it and re-emitt it to the TV set as the same code sent by the "Video/Mode" button on the TV remote.
Volia! I can now change "Video/Mode" using the TiVo remote's "Window' button, and throw the TV set remote in a drawer forever.

Basically, I need an IR receiver and Emitter that can take code "A" and retransmit as code "B." But, I must also figure out what code "A" and code "B" are from the two remotes (or at least "teach" the codes) to the device.

What can you A/V guys suggest as a good system that can do this?