See help for "About array formulas and array constants" subtopic "Using
array constants". The {} syntax is limited to constants, so you could
do =LINEST({3,4},{1,2}), but not what you attempted.
=SLOPE(E2:E4,D2

4) and =INTERCEPT(E2:E4,D2

4) will ignore non-numeric
values in row 3. If there are numbers there, you could adapt to ignore
row 3, as in =SLOPE(IF(ROW(E2:E4)=3,,E2:E4),D2

4) etc.
http://groups.google.com/[email protected]
gives ways to calculate the other statistics returned by LINEST when
fitting a straight line.
Jerry
Excel MVP