both have resolution of 1920x1080, but 1080p is progressively scanned as opposed 1080i which is interlaced.
1080i = all the odd (or even) lines are painted on the screen in the 1st pass, then the even (or odd) are painted about .03 secs (approx) afterwards in the 2nd pass.
1080p = all lines are painted together in one pass, which gives a smoother image.
If it was just a general question, there is your answer. If you're thinking of choosing a tv, don't bother with 1080p, there's nothing that natively broadcasts in 1080p, not for a long while i'd imagine. There's also hardly any discernible difference between the I and P.
Personally, i've just bought a LG 42PQ6000 plasma, and chose 720p (1080i) but with a refresh rate of >100Hz, rather than 1080p and 50Hz (within my budget).
Hope it helps.