To arrange for accommodation we suggest to book a room at one of the Cambridge colleges
The nearest college to the Institute of Astronomy is Churchill College, which is ~10 mins walk to the IoA. Rooms can be booked using this link:
https://www.chu.cam.ac.uk/conferences/services/bandb/
Other options for college rooms can be found here:
http://www.universityrooms.com/en/city/cambridge/home
Alternatively B&Bs and hotel options can be found at:
http://www.visitcambridge.org/accommodation/
Summer is a busy time in Cambridge so please make sure you book early.