There must be an easier way to do the same thing (If you've got a better one, e-mail it now), but it really works. Areas shown in red will be filled in by the computer. You only have to fill in green areas.
This table works under MS Excel 97/2000 (c). It does work when:
a) a student doesn't take your exam (he doesn't get a zero for this exam, but a special warning appears on the table to let you decide what to do).
b) you give different weights to your tests.