http://hometheater.about.com/od/tele...80ivs1080p.htm
Check out this link
1080p is beautiful, i have a 1080i Plasma and a 1080p Lcd and the difference is big, i didn't think it would be but it is.
I think in a nutshell (correct me if i'm wrong) P (Progressive) refreshes the signal sent to your TV more times a second than I (Interlaced) giving a more clearer picture.