well - it is an existing deck with nails already in it. Do i need to hammer them down? and then take a punch and make them countersunk?

Problem with my deck is the boards are diagnanol and go into the the side of the home. seems like I wont be able to do the length of the board way you suggessted.

here is a picture of the deck.

and a picture of the nails:

You don't really need to countersink the nails. The only thing that is important is that they are not sticking up so that they will rip your sandpaper and/or rip up the pad on the sander.

what type of stain do I need to use after sanding? Would like to put alot of coats down and then put a waterproofer down. Suggestions?

One Time remover/sealer.

http://www.onetimewood.com/product/014/OneTIMEStainandSealRemover.aspx

But, I am no pro on this, but would have concern about how you are going to 'expand' or seal the natural cracks that have developed with drying out.

??

I went to homedepot to rent a vibrating plate sander and they did not have one. They only had a drum sander or a random orbit sander that you use on hardwoods inside. They would not rent it to me for a deck. Where would I rent this thing?

hahaha, thats funny. Ya just go back another time and get it. I used one from home depot last year, with great results might I add!

a drum sander or a random orbit sander?

I am looking to sand my deck and wanted to know out of a drum sander, random orbit sander, or a vibrating plate sander which is the best and why. Thanks

You might consider pulling the nails at this time, where it's easy and replacing with screws.

Do not sand off the finish of the nails or screws.

A Random orbit sander is fine, just much slower. A drum sander, you need to avoid cross grain sanding. A vibrating plate sander is best, with touch up areas with a pad sander or orbiting sander in those places you cannot get to.

If the porch or deck is looking a little worse for the wear, a good sanding might be in order. Not only is sanding an essential step if you plan to add another coat of paint or stain, but it can help you enjoy your deck much more.