17 July 2012
Since you earned LTCG in F.Y. 2011-12, you should show the details in the ITR relevant for F.Y.2011-12(A.Y.2012-13). However, since you have invested the money for purchase of new house within the stipulated time you can claim exemption u/s 54 in this return itself, as the dedution is claimed against the specific income of this year.
17 July 2012
For Purchase of new house-within one year before or two years after the transfer. For construction- within three years after the transfer. But if you have not invested the whole gain before the DUE DATE of filing your return, it shall be deposited in branch of a public sector bank under Capital Gain Account Scheme, 1988, before due date of filing the return.