The next deadline for applications for Scientific Associateships ( http://jobs.web.cern.ch/join-us/scientific-associateships), intended for extended stays of established scientists, is 13 March 2014.
For details see the link on the left.
It seems to have become common practice for certain visitors to just show up without an official affiliation with CERN TH, and demand and obtain office space. In view of the very high demand these days this is not acceptable. Only visitors whose request has properly passed the relevant selection committee will be granted a desk.(*) This applies also to Ph.D. students joining their supervisors. Self-invited visitors are otherwise free to use desks in the library and public PC's.
(*) In urgent cases of short notice an endorsement of a staff member is sufficient. However, an office cannot be guaranteed if the request is made less than a month ahead of time.