creating a function that maps to a large spreadsheet

I have a complicated Excel spreadsheet that essentially looks at 1 cell and calculates an output (it uses iteration to converge to the output value).

The problem is I have a lot of data I would like to run through the spreadsheet, but I don't want to do it one by one. I would somehow like to "call" the spreadsheet, insert the input, and retrieve the output, and do this multiple times. Does anybody have any tips or example VB code that can do this?

Thanks,

K Christman