recording volume external microphone

not sure if what im tryin to do is possible but let me tell you what i want to do. my daughter is singing some canned music in church i want to record her singing live. at home ive hooked up a mic and went into 1/8 input on side of computer and created new track in garageband hit record and just did the testing testing 123 thing and it recorded fine, good volume (with no interface). i go to the church and try to go from the headphone jack on mixing board to the computer. i'm getting signal but it doesnt have any volume (very faint).how do i get the volume up? next thing is i dragged some pictures from iphoto to imovie and put the canned music with it and made a neat little video that i can show while she is singing. problem with that is tryin to show video and record at the same time. have thought maybe doing imovie with voiceover? i also put movietrack into garageband but cant figure out how to show it on projector and record live singing at the same time. it shows movie preview in garageband but i cant get it to projector which would slove all my problems (except for mic volume). im playin with this stuff while she is practicing and the best i can figue is start recording in garageband (if i can get volume) switch to imovie and then start video. my problem with that is not being in sync and tryin to make a good presentation (eg. when program is not running you can see the desktop on projector screen). ive also dragged movie into keynote and thought about recording narration while presentation is running but the picture is small (imovie shows bigger picture)and presentation has red dot in upper left corner people will be seeing. i know there is probally a program to do all this but im poor and cant afford it so any ideas would be helpful. thanks paul