Doubt about tax benefit from home loan.

I am staying in rented accommodation and I have booked a residential flat which is likely to be completed and given possession in January/February 2013. However, my EMI due to home loan had started in July 2012. Can I claim full benefit of interest paid and principal paid for the entire period (July 2012 - March2013) or will I be entitled to tax benefit only for the months remaining in FY 2012-2013 after getting possession for AY 2013-2014?

Second, can I claim home rent deduction (I receive HRA) simultaneously with home loan benefit? Thanks.