Assuming that you only started during the tax year 6th April 2010 to 5th April 2011, the £1400 that you owe will be for that tax year, as you would appear to have made no payments on account for this period.
The 2 installments of £701 each due in January 2012 and July 2012 will be for the tax year 6th April 2011 to 5th April 2012, by which time you will have received payment and hopefully put adequate funds away to pay the tax bill. Although with Self Assessment the final tax settlement is made in arrears, it is always advisable to save some of your income to cover the Tax and National Insurance that will be payable eventually.
When you make your Self Assessment return there is a section where you can request to make smaller or higher payments on account, but it is better to err on the higher side, then you can't be fined and can earn a small amount of interest instead.