Are you seeing the error “Cannot play media. You do not have the correct version of the flash player. Download the correct version” on the BBC web site or on YouTube “Hello, you either have JavaScript turned off or an old version of Macromedia’s Flash Player. Get the latest Flash player”?
I have been on my Dell Mini; I suspect the problem was the upgrade route I took from XP-Home -> IE8 Beta ->XP Prof meant the registry was a mess. Repeated re-installation of Flash and Shockwave had no effect.
After much fiddling I fixed it by downgrading to IE7, running the Abode Uninstaller, the installing Flash and upgrading to IE8 again. However I suspect I did not need the IE downgrade first, but I had done this previously.
Hope this saves you some time.