Windows7 + Office 2007

I have a spreadsheet that lists a variety of companies in a column, each with its own row. Along the row of each company are columns with various actions categories. Within the 'action taken' cell is a date--the date upon which I had taken an action. I would like to have a mechanism within these dated cells that would allow for an alarm to 'wake up' the spreadsheet and tell me, "ah! n days have passed and now is probably a good time to get back with this company."

I do not see anything within the spreadsheet absent programming that will do something similar to what I want...am I missing something?

Thanks,

Mark