So how did I do it?  Here is a step by step tutorial in case you want to try it too: Step 1: Remove the Rails Remove the rails that are attached to the wall. There are little clips that screw into the underside of the stair rail that are held by two screws.  Unscrew those and lift off the rail.  In my case the hardware was all brass (of course) so I had to deal with that right away.  
Step 2: Update the Hardware
Rough up the hardware with some 180 grit sandpaper and spray it whatever color you want.  I chose brushed nickel to match my door knobs and other hardware:
Then tape off around the brackets that remain attached to the wall. Don't remove them since they should be screwed into a stud and you don't want to risk loosening them up when you take them down and put them back up.

You can use painter's tape up around the bracket and then tape up paper, sheet plastic or a drop cloth a few feet around each bracket to prevent spraypaint from getting on anywhere else.  Also be sure to put a drop cloth on the floor below the area you are spraying to catch any falling paint spray.
Depending on the color of the hardware and the color of the spray paint you may need a couple coats
Repeat on all the brackets.  Don't remove the paper or tape until the paint is completely dry, in order to avoid scratching the fresh paint.

Step 3: Sand the Rails
It is a good idea to do as much of your sanding outside if it is possible.  I was able to remove two rails from my stairs completely and I took those into my driveway and went after them with both my palm sander and by hand.

Start with a lower grit sandpaper (60-80) in order to remove the finish:

The rail on the right has been sanded once with 60 grit sandpaper. You will notice that the sheen is gone and it will feel almost 'chalky' to the touch.

Another tip I have for the sanding step is to minimize dust by taping off/closing any vents anywhere need your work area.  I had an air intake right below where I was sanding.  The last thing I wanted was fine sawdust to blow all over the rest of the house so I taped a sheet of paper over it and the dust stayed contained to the immediate area:
To apply the stain you can either you a cloth (which is messy unless you are wearing gloves) or my tool of choice, a foam applicator.

A nice thing about using the foam applicators is that they are inexpensive and can be thrown away after you are finished with the project.  In between coats I store them in a ziplock bag and they stay wet so you can reuse them for additional coats, but at the end of the project, instead of cleaning them up with mineral spirits (since the stain is oil based you cannot wash them in water), I throw they away.

I actually use two applicators, one to wipe on the stain pretty heavily, and one to wipe it off.  With the stain I was using, I found it worked best to apply the stain pretty heavily, wait about 10 minutes until it was a just starting to get to sticky and then use a second applicator to wipe off any areas that were drippy or too heavy.  Per the manufacturer's instructions I never allowed any excess stain to sit on the wood. Always remember to wipe with the grain of the wood and from the darkest areas towards the lightest.

First coat of stain

Second coat

Third coat

It is Poly Time!

Can it be? Is that beautiful oak?

Painters tape along woodwork

I used oil based Kilz primer for this project, although because you have sanded down to bare wood and because the balusters aren't high traffic areas, you could use a latex primer if you choose.  I used two coats of primer and sanded (220 grit) in between each coat.   Make sure you use a good quality brush for the smoothest finish, especially on the tricky nooks and crannies of turned rails. (I used a Purdy angular trim white china bristle which is the gold standard for a good finish when using oil based paints.)

After two coats of primer: looking good!

Step 8: Touch up Finally! The last step.  At this point there is probably going to be a few drips, splats or smears of stain, paint or primer on some of your walls.  Make sure you touch up those spots if you want to give this project a professional finished look.  Because the stain color I chose was so dark, I actually had to touch up my mistakes with primer first and then paint over the primer with the wall color.  And there you have it!   For me, this project only cost me $4.79, the cost of a can of stain. The spraypaint, sandpaper, primer, paint and painting supplies I already had on hand.   That is a great deal since I think it looks like a million bucks!