Now that I've already done it(!) I got to wondering whether there was an easier/quicker way to do what I've done...
I needed to create a grid where users could enter numbers, at the end of each row was a total field which was the sum of all the values entered in that row.
4 rows with 14 values and a total on each. I don't think I could have used a repeating table for the rows as the condition for putting values in the row differs from row to row.
Only way I could see to do this was to create a table and then place a small text box in each cell. Then a formula in the last box.
I couldn't import the form in from Excel as we don't use Excel 2010 here (but do Infopath 2010)