Popup help from Dashboard

Can someone advise me on creating some kind of Pop-up help screen from the Dashboard to provide special instructions for a plugin that is difficult to understand?

I’m working with a Calendar plugin that is excellent overall (Kieran Oshea) but that has a clumsy interface for entering repeating events …it’s very frustrating for users because it’s counter-intuitive.

So I want to put a special HELP link on the Dashboard for that calendar Plugin – when clicked it would either pop up a new window or something similar. The special instructions needed are so extensive that they won’t fit on the existing dashboard page.

Any advice would be appreciated.