Starting an innovation week at work here. Good ol' Excel project! So here's what we want. We want to be able to create user defined functions in Excel, just like Excel has the `SUM`, etc. we want to make our own.

These UDF's would take Excel data in, and they would then pass that data to a Web Service which would do what it needs to do and then return the data back. I know how the Web Services will act, but what I need some guidance on is preparing the data in Excel, setting up the UDF's, and dealing with the sending/receiving of the data in Excel. I've never done any Excel programming before.

At first glance, it seems I might not need to do any VBA work, and that I could almost create a plugin for Excel (generate a .xll file from C#), and then go about it this way, but I'm not really sure how this all works.

Am I approaching this right? Are there any other things I should keep in mind? Is there anything I should read up on (any good links)?

Thanks.