Static Date Time stamp for cell entry that doesn't require changing iterative setting

I'm looking for a formula or a way to write a new function for date/time stamp. When an entry is made in cell A1, I want cell B1 to populate with the date/time of the entry, and so on down the column A for each entry (and not update when the workbook is opened). I'm putting this into a workbook that will be used by a beginner excel user. I don't want to make them change their 'iterative calculation' setting (I've seen a circular formula that does work on several websites). I think there is a way I can write a new function though and embed it into the spreadsheet. I'm using excel 2007 but the users may have earlier versions. Thanks for your help :D

The alternative to using an iterative formula is to use a macro. See the attached.

Macros must be enabled for this to work.