Wikipedia gives the calculation of t statistics for several different cases. http://en.wikipedia.org/wiki/Student%27s_t-test#Calculations
Given a t statistic, you can find the corresponding probability using a lookup table or a calculator like http://easycalculation.com/statistics/p-value-t-test.php.
You may find an introductory statistics text helpful.
It is pretty straight forward if you have the Means and the SD. To save time you can use any of the statistical software package. Here is a link to a free software that can do the job for you