Nobody seems to have mentioned this, the Yellow, Red and White cables can only transmit standard def images, 576i.
To get the full hidef image out of the Ps3, or Xbox360 for that matter you need to connect it up by HDMI, Component (Blue. Green. Red cables) or VGA.
The same goes for your DVD player if you want progressive scan one of the three connections above, not scart.
So connect the PS3 via HDMI and you will see the full 720p hidef image, most PS3 games are 720p anyway so you are loosing nothing only having a 720p screen. But you are loosing a great deal using composite.
Just buy the cheapest HDMI cable you can find, they are digital cables so it will either work or not work.