The picture Dawn sent is posted below. If I understand correctly Dawn, you basically want a field similar to the Related to Campaign field on your screenshot, but for Opportunities and Cases on all activity screens? The screenshot you sent me looks like the Google Gadget and unfortunately at this time the Google Gadget cannot be customized. You can however achieve this in regular Method.
If you would like to try and customize this yourself, I would suggest copying and then reverse engineering the screen to try and learn how the Related to Campaign field works. However, after taking a quick look myself, it seems like it may be a complicated job. I would suggest contacting your consultant. (I know you've already been in touch)
If you would like to learn about customization we have some customization webinars here near the bottom of the page. I also recommend checking out our Method Solution Providers.
Best,
Jason