Internally we do not use Macros in order to maintain portability between applications.
Well, it's in the nature of macros to be compatible with the underlying application only (Excel in this particular case). Furthermore, Excel is compatible with the Windows operating system only. When someone decided to write a particular software as Excel macro, he or she decided to use Excel, assuming that Excel is "standard" for the time running that macro.
I would love to convert this spreadsheet to work in Open Office but do not have the expertise.
You need the expertise to understand every detail of the VBA program in Excel before you can start rewriting a similar thing for another application.
Is this the only thing that binds you to MSOffice? Then it may be reasonable to pay someone for the transition.
The US Federal Reserve has banks using a macro-laden Excel spreadsheet for submitting Canadian Cash Letters.
What tells you that they will accept your self-made Calc sheets with StarBasic macros?