The Central Science Library can now provide wireless access to the internet via the University Lapwing wireless service. The access point is in the main reading room on the 2nd floor but you may find that can get a connection elsewhere in the building.
This is service is available to all current members of the University via RAVEN.
Non University members, alumni or anyone who does not have a RAVEN account can still use the wireless service by creating a Lapwing ticket.
See http://www.lib.cam.ac.uk/CSL/wireless.htm for more details.