There are a multitude of sites to help with retirement planning. Here is a samples:
http://www.troweprice.com/retirement
The annuity formula in the book is actually called an ordinary annuity. This is the situation where the payment is made at the end of each payment period. There is another type of annuity known as an annuity due which deposits the payment at the beginning of the payment period. This site provides a calculator of this type of annuity:
http://www.moneychimp.com/articles/finworks/fmbasinv.htm
