populate a cell once & using TODAY() inside function.

Greetings,
I'm starting a project where Excel will be used as the main UI for defining a table of data. I'm expecting to define a "template" - xlt i guess - that users can open and save as an xls, without over-writing the template. Users will populate the spreadsheet with a lot of help from user defined functions.

I'm just getting started and would like to populate a particular cell with the current date, but only the first time the sheet is opened. I tried checking whether a cell was empty before assigning a value to it, of course this meant recursion!

Also: It might be nice to use the Today() function inside a UDF, but TODAY isn't a member of Application.WorksheetFunction - is there no way to reference TODAY() from within a UDF?

Thanks/Cheers!