newbie needs help with screen size

hello everyone, i am fairly new to this forum and i am new to projectors. i picked up a Infocus 4800 and 73" screen from a friend of mine really cheap. he had it in his living room and it worked fine for the 73" screen. my problem is due to my playroom/theater room having a little less than 8 foot ceiling, i need to ceiling mount the projector over the seating area towards the back of the room. which will end up being approx 19 feet. i held the projector in the approx place it will be mounted and the picture came out to be 100" across.

so after all that, the projector is 16:9 default. i plan on using it for digital cable, dvd's and ps2/Wii. so most will be widescreen, but there will tv broadcast that are 4:3. my ? finally bolis down to what size screen do i get?

sorry this so long, thanks in advance.

thanks for that link, there seems to be alot of info there. so it looks like if i went with 100" x 75" screen that would cover 4:3 and 16:9. i know most will be 16:9, but there will be some non-HD cable shows/sports at some point and time. thanks again.

please if anybody is or has been in my situation, please share your experience.