Run!, run away! and flee! from the idea of using spreadsheets as statistical analysis tools.
Ok, on a little more serious note, read this article on Spreadsheet Addiction to get a better view of why you might want to consider using other tools besides spreadsheets. In the long run (even the medium run) you will gain more by learning to use programs designed for statistics to do statistics.
Then next time someone tells you that they want to be able to do everything in Excel (or other program) then challenge them to use it as mail client and word processor, that they should use only excel to write their next article or report. If you really want to push this into more obvious sillyness then challenge them to use Excel to cook their dinner or wash their car. When they react that your challenge is silly ask them why it is any less silly to use a spread sheet for statistics when there are programs specifically designed for that which do a much better job (again see the link above).
tdist()function isn't available on Google Spreadsheets, but can be programmed in JavaScript. – smillig Dec 20 '12 at 17:18