Excel does not natively offer calculus functionality. Some functions
can be integrated in closed form.
http://integrals.wolfram.com/
or
http://maxima.sourceforge.net/
may help identify some of these if your calculus is rusty.

Where closed form integrals do not exist, there are many methods for
numeric integration.
http://www.stfx.ca/people/bliengme/E...UnderCurve.htm
implements a couple of simple methods in Excel. Chapter 4 of Numerical
Recipes in ... goes into more detail in C, C++, Fortran, or Pascal (out
of print). There may even have been one in Basic at one time. The C
and Fortran versions are available on-line
http://www.library.cornell.edu/nr/bookcpdf.html
http://www.library.cornell.edu/nr/cbookfpdf.html
Fortran is probably easier to translate into VBA than C.

Jerry