Yes, you can do that. Add a text box to show the sum of the 8 values selected
from the drop downs.

1. Right click the text box and select 'text box properties'.
2. There will be small button named as 'fx' to the right side of the 'Value'
textbox (in the default value section). Click it. It will open another small
form.
3. Click 'Insert field or Group' button and select the first drop down. Add
a plus sign manually after the added field. Again click the 'Insert field or
Group' button to add the second drop down. Repeat this step to add all the
drop down boxes. Your formula will look like this:
field1 + field2 + field3 + field4 + field5 + field6+ field7 + field8
4. Click Ok twice to close the open dialog boxes.
5. Preview the form, select values in dropdowns. The text box will show the
sum of all the values.

SSA
MOSS MVP