DMS has published a set of macros for use in Excel or OpenCalc for working with ocean waves.  Macros include items like converting between various properties of regular waves, inputting various wave spectrums, spectrum integrations, encounter frequency, and reproducing a time history from a given spectrum.  All macros are implemented just like any other spreadsheet function.  It is entered as a formula into a cell.

You can view further details and download the macros under:

Tools->Macros