The public Athena clusters cannot be reserved, however there are some options. First, for groups of 2-5 people (a freshman seminar, for example), there is small-group study space in 56-129 and W20-575, available on a first-come, first served basis.
IS&T maintains two "electronic classrooms", with Athena workstations, video screens, and projectors. Room 1-115 has 22 Athena workstations (plus one instructor's workstation), and room 14-0637 has 17 workstations.
The electronic classrooms can be reserved through the Registrar's Office using normal classroom reservation procedures.
The Office of Educational Information Technology maintains several "learning spaces", including the 37-312 Windows Cluster and the 26-129 New Media Center. Each of these rooms has different reservation policies and procedures, which are documented here.