Problems when developing a Salary Payroll

sir,

am a Programmer and am using ASP.Net in visual studio 2008 and MySql as database. currently am writing a payroll software but i got hooked on the way. i wish to command the system to evenly divide certain amount into number of months,e.g deduct 30000 from person salary systematically,i.e.3000 every month for 10 months

thanks sir,

walepat