About 3/4 cup corn sugar (dextrose) to 5 gallons of beer. A little more or less won't hurt it.
The "Prohibition Method" (what Papazian calls it) of priming each bottle individually has two small problems associated with it. First, it makes sanitation more difficult to control. Second, uneven amounts of sugar in each bottle, potentially leading to under or over carbonation.
If you have two carboys (or pails), when it's time for bottling you can pour your sugar solution (your dextrose boiled in water) into the empty one and then siphon the beer into it. Or you can add the sugar directly to the entire batch if you take care not to stir up the sediment at the bottom (I do it this way when I'm feeling lazy).
Know I'm a bit late and its a moot point, but perhaps this may be of help in later batches.