don't sweat it. they just want to figure out what area they can place you in and probably get you to buy a 10-15 dollar shirt from their hospital that says "volunteer."
seriously though, i never got much out of my volunteer experiences within hospitals. it was kinda like, "follow that guy around and file his papers........... go watch them do some stitches........ oh yeah, we got lunch over there if you want a bite."
subsequently, i got fired from volunteering for skipping twice (too early on a friday morning after going out).....i didn't know it was even possible. so fourstar, as long as you show up, they should love you and it won't be a problem.