Get excel macro to email reminder

I have a basic spreadsheet with several columns and rows of data , (each row for a "contact" ), formatted to a table. Column L of all rows is a date. A new row is inserted for every new "Contact"This date in column L is entered manually and will be a set amount of days from the current date the sheet is being edited. Lets say you worked on the worksheet on Jan. 1 2011. The date in column L would then be entered as Jan. 8, 2011. This is to set a time period.
When the actual date reaches the date entered in column L, I want an email to be sent to an email address the next time the worksheet is opened. This address stays the same. It is used as a reminder to the user of the worksheet that a week has passed since the original date was entered.
I also need the subject of the email to be the contents of the cell in column A ,of the row where the date has expired. The body of the message would be a string, ie " This is a reminder to check with this contact"
Once the date has expired, nothing would happen.
Again, this worksheet is opened almost daily (except weekends) so I need the macro to run every time the worksheet is opened.
Column L is formatted to Date , mm/dd/yyyy