Engineering Interpolation x to y?

Hi,

If you will excuse the word, QuattroPro, has a very
nice function that will interpolate (like reading
a graph) to produce an interpolated Y for example
if the two columns of selected cells were:
2 2
4 6
9 9

and you entered 3.1, the answer would come back 4.2

Has anyone seen a canned add-on function for Excel that
does this kind of interpolation?

Thanks