From April 6th 2010, you can save up to £5,100 in a fixed term Cash ISA, where you will pay no tax on the returns, your interest rate will remain the same for the duration of the fixed term, and your capital will not be at risk as it is in a Stocks and Shares ISA.
The remainder of your ISA allowance - £10,200 from the 2010/2011 tax year – can be invested in a Stocks and Shares ISA, either fixed term or not, where you could earn potentially higher interest in return for taking greater risk.