There are many ways to make a sprite sheet,
I myself use photoshop/gimp to make my (new) spritesheets,
i simply make an canvas with the size of 98x128 pixels(pixels are an measurement option in PS/Gimp)
and then(for characters) import an template onto it so that i can
add the hair,armor, etc. myself without worrying about pixel/character positioning at all as the
so called 'base characters'' are already on it
To rip a certain part from a (example): big sprite sheet like ''people 4"
and i would want only the soldier part of it, i use the rectangular selection option
in GIMP to ''pull a line'' over the soldier set and then adjust the size to 98x128 through the
so called ''Tool options''
then i only need to copy it and past it on a blank 98x128 field or on a template
(like mentioned before) and then i'm done
Sorry if i misunderstood, i'm a bit 'slow-getting'' today