Have you got an Xbox 360 Live Gold subscription? (£39.99 for one year at Argos. A little cheaper from some online sources). If not you can't access Sky player.
Hi - the boy has some super-duper subscription thing (I presume it's the best one as my husband sorts it out). We can see the sky player thing but it is asking for our Sky id (we have a Sky box) but I don't remember registering one.