Excel add-In: anybody done with Delphi?

Has anybody written a Excel add-in (XLL) with Delphi? Have you ported
the C headers and function, which are part of the Excel Resource Kit
from Microsoft, to Delphi? Did you encounter any problems?

I'd be glad to hear anything that could help me building the add-in. It
doesn't seem to be that difficult. But I don't want to invent the wheel
twice.

Regards,
  Manuel