Hallo, LR. Here goes:
Open Firefox (it also works in Chrome and Safari, so if you use either of them, open up in the browser of your choice). Google Media Hint. You should get a choice on Google for your browser, so click on the appropriate one.
It should look like this on Google:
In the case of FF, click on "Media Hint - add-ons for Firefox". You should get this page:
Now, just click on "Add to Firefox" - and that's it. It's added to Firefox as an add-on instantly. Go the BBC iPlayer, and off you go! Let me know if it works.