Simon,
It depends how non-contiguous the range is.
If it is every nth column (or row) it is very simple. Then you SUMPRODUCT across all columns (rows) and use the MOD function to isolate the columns (rows) that you are interested.
For instance, let us assume that the range to be tested is A2:Z2, and we have say a date, then a name, then an amount, you can sum the amounts for say Simon like so
=SUMPRODUCT(--(MOD(COLUMN(A2:Z2),3)=2),--(A2:Z2="Simon"),B2:AA2)
