Excel data extraction macro needed

Hello,
Hie .I am working on a project in which l have to compare dates in excel and enter the difference (in days)in time in a separate column .l am looking for a macro which can extract data from text ie if the end date of a task in a project is say 2008/08/10 i n a previous project review then it becomes say 2008/10/12 .l need to write a macro which can tell me the difference in figures ie it subtracts the earlier date value from the latest one to give me the time difference in days.Is it possible? Is there anyone who can assist?

Thanx

Theo