Lucy,
With brush on paint, you do not have to worry about over spray on your baby....
This is a diry job. Wear gloves or something similar. If you have long nails the brake cleaner will take off your nail polish..
Get a couple of cans of brake cleaner and some small wire brushes. Steel and brass work well. LOTS OF RAGS...
Remove your wheels and calipers the pull the brake pads off. Mark them so the go back on the same way/side. Then put the calipers back on the wheel without the pads.
This allows a much better way to clean the calipers without trying to hold them.
DO NOT LET THEM hang from the brake line...
Start cleaning, make sure to clean around the caliper piston. This will make pushing the piston back in a lot easier, since they will drift outward. When they drift, you will not be able to get the caliper w/pads back on the rotor with out pushing them in a little bit.. Do not use a wire brush on the piston rubber.....
Look here: http://www.z4-forum.com/forum/viewtopic.php?f=15&t=4379
You may want to do two wheels a day. Depends on how long it takes the paint to dry. I did fronts on Sat, and the rears on Sunday.
If you are planning on using a spray paint, make sure you mask off the pad surface of the rotor and the rubber piston portion of the caliper.....
I just finished washing my car this evening, and now one year later (after painting), the calipers are still bright red and the hubs are shiny black, like in the pictures....

Of course my car gets washed twice a week...