A bit of advice: stick with 720p. 1080i is NOT a better resolution that 720p, because the "i" in 1080i means interlaced, while the "p" in 720p means progressive. What this means is that while you have 1,080 vertical lines of information with 1080i, only 540 of those lines are visible on your screen in each alternating field within a single frame, as opposed to 720 vertical lines of information being visible at all times in every frame with 720p
It is a common misconception that people make, thinking that 1080i is better than 720p, but it isn't. There may be some people who will argue that I am wrong, but I work in post production for television and deal with HD formats all day long. When you're dealing with a lot of movement on screen (ie - a sporting event or videogame) 720p will always look better than 1080i. Period.