Well, the wiki is up and running and has withstood a day and a half of kids signing up. Good news: it works, and works from any computer.
Bad news: it is SLOW. Don't know if it's just pbwiki, but as I'm typing in each child's info, we have to wait 5-10 seconds for just about every field until the computer can catch up. It's just as slow from my home computer, so it's not the machine. Might just use Excel next year.