Can you tell the difference between an HDMI cable and a Component Cable?

HDMI has flat, rectangular ends with tiny prongs inside like a USB cable but a component has usually 3 round heads at each end, 3 cables tied together

HDMI cables are just one cable with a rectangular input and output. Normal components have one rectangular side, then splits into 3 (sometimes six if you have a slightly fancier one) cables with red, white, and yellow round connections. You would very easily be able to tell the difference. Sony-manufactured PS3's come with a basic component cable set. If you want to by an HDMI cable, you can often buy gold-tipped (better ones) for $10-20.

HDMI cable offers HD film / cinematics. Since the gameplay isn't HD, you wouldn't tell a difference between having HDMI or a Component cable while playing. The difference is when you are watching HD movies or the cenimatics of a game.