if i try to play a 1080p blueray film what happens does my tv play 1080i or does it go down to 720p new to all this thanks for help in advance. my tv is 1080i max.
If your TV is capable of 1080i then the Blu-Ray player should play the disk at 1080i. The player may have an option to let you pick what signals (1080i, 720p etc.) it outputs but if not then it will choose the highest (1080i in this case) level your display accepts and output at that resolution.
Try both because some displays will drop the resolution to something like 540p then upconvert to 720p when getting 1080i as a source.