I'm not real clear on what you want to do here. Are you already in a play PS3 activity so you are sitting at the XMB and you want a macro that will move around the XMB and select the Blu Ray movie button? If so that would be very hard to do because the PS3 keeps track of your cursor location so you won't be starting from the same location all the time. You would have to make a macro that moves the cursor all the way to the left, then move it right to the movie icon, then the cursor would have to move all the way up under the movie Icon, and then move down to the Blu Ray icon and hit the X button. It could be done, but it would be a very long macro.
If you are just asking how to set up your PS3 activity you will want to set up a "Play A DVD" activity and tell it you use your PlayStation 3 to play a DVD.