dunno if anyone can tell me or maybe someone with a ps3 and knows their shit can clear it up.

Hooked up my ps3 last night to my TV, Its a sony 106cm HD LCD TV, has the HDMI ports. The ps3 does not come with the HDMI cable, only RCA cables so i hooked it up with them, put in my game NBA Street, fired it up, went into the game, graphics are awes, but the graphics are jaggered along the edges of the people/scenery (looks like a pc running a low resolution, liek when u go into setting and change the resolution.), i have seen this game in videos and in the shops and is alot smoother and clearer. My question is is this because of only using RCA Cables, they support only 540 resolution where as HDMI cables on the lcd tv are 1080p. Is this this the cause of the poor screen quality? or am i just being paranoid, any suggestions? should i get the HDMI Cable?