A message popped up saying I had to re-register my domain. I did so and the hosting account got created immediately. Weird.
Thanks for the help! (And to x10 for creating such a great free service.)
Edit:
Okay, I made a domain name separate from x10hosting.com (ie
http://site.com/ rather than
http://site.x10hosting.com/). The control panel says it's done, but I when I try to access it pops up with an "address not found" message.
Do I have to buy the domain?