Ask YC: First and Last Name + Username vs only Username?

We are finalizing our sign-up process for NIXTY (www.nixty.com). Broadly, our market consists of educators, learners, and academic institutions. We subscribe to the belief that getting users easy access is hugely important. However, our target market isn't the most technically advanced. So, we are struggling with what information to gather on the initial sign up page. Should it be: First Name Last Name Username Password Email

Or...should it just be: Username Password Email

One person thinks that educators and students might feel more comfortable putting in their first and last name and then choosing a username - partly b/c the idea of a 'username' might not be immediately apparent w/out the first and last name. In addition, the first and last name would be gathered on the second page. The other person feels that most people know what a username is, so the first and last name isn't necessary on the sign up page.

One last thing to keep in mind, the username is the person's unique identifier and will be part of their URL.

Any and all thoughts are welcome. Thank you.