Online communities dedicated to the creation of fanworks (e.g., fiction or art inspired by media such as books or television shows) often serve as communities of practice for learning communication, artistic, and technical skills. In studying one successful fan fiction archive that was designed and built entirely by (predominantly women) fans, we observed processes of legitimate peripheral participation (LPP) in which some of these fans began in peripheral roles and came to be more involved in the technical aspects of the archive over time. In addition to outlining positive outcomes, we discuss the challenges of supporting learning within this CoP, particularly with respect to the burden on experts. We discuss potential implications and solutions for the problem of expert scarcity in CoPs, and propose that LPP within fan communities can be leveraged for broadening participation in computing among women.