This has to be one of the most popular questions business owners ask their accountants, purely looking at it from a financial perspective I would recommend trying out these free calculators:
http://listentotaxman.com/index.php
This allows you to calculate the Tax and NI payable on Salaries
This link calculates the tax on dividends (Dividends are paid after the company has paid Corporation Tax which is 21% for small companies)
steve@bicknells.net