My dad postulated an interesting question upon me and I know nowhere else to turn but Toms hardware. He wonders if a blu-ray player will display a movie from a blu-ray disk to his 720p television properly. His concern is that blu-ray is 1080p and would not scale properly to fit his TV set.
A bluray 1080p will work fine on a 720p set. You just miss out on some of the extra detail you get from the higher resolution. 720p tvs still support 1080i which means it will play any bluray, just not at the highest resolution.
Otherwise go get a decent player and enjoy and bluray movie.