The iPad cannot play Flash videos natively - Apple decided not to support Flash and this has been well publicised - you can see quite a lot on their website about this including a detailed technical White Paper on why they took that decision.
There are several third-party browsers that 'sort of' support Flash by hosting it on their company web servers but the results can be mixed and are not always entirely satisfactory. You'll find literally dozens of threads on iPad Forums about the Flash issue and how members have found workarounds. My favourite, currently, is to use a remote PC access program and simply host any Flash sites on my PC - the app I use is called Splashtop and you'll find lots of comments, too, about this app in iPad Forum.
Tim