Simple...you CAN'T do this via iplayer, ITV player etc on the PS3 or similar device such as TVs and bluray players equipped with the players and only some limited content via a computer is available to view live with the recent olympic coverage providing the largest amount of live content yet seen on any of the BBCs web services.
Shows usually take about 2 hours to appear on BBC iPlayer after being broadcast and MOTD (saturday eve) is not available atall to view via iPlayer due to the restriction placed on the BBC when it won the bidding to show highlights but will be available from next season when the new deal kicks in, currently only MOTD2 is available to watch via iPlayer and so you will have to watch it live or miss it entirely. It's also worth bearing in mind that MOTD 2 doesn't go up on iPlayer until the tuesday after the show goes out again due to the bidding agreement.
You will have to keep your Freesat service for the forseable future i'm afraid if you want to watch live tv and the BBCs MOTD coverage.