First of all, welcome aboard Jim.
And we can help you to replace that post, you just need to get the confidence up, and send us a few pictures if you can.
This is actually an easier job than most.
A car jack, a hand saw, and an extra 4x4 are the basics you will need.
Adding pieces to a rotten board only prolongs the inevitable, and the structure suffers because it has also most likely sank down with the rot.
Read through this link, post a picture of the post and what it is supporting , and we will help because this is DIY.
How to Replace or Update a Porch Column | eHow.com