Question validating start date and end date in grid view

[Mythri]

I have a grid view which is editable.There are 10 rows with column "start date" and "end date".
4/1/2011 17/1/2011 (valid-existing row)

1/2/2011 3/3/2011 (valid-existing row)

3/1/2011 21/1/2011 (Invalid - edited row )

I should check whether there is any row having start-end dates lying within the existing date range and if there any i need to show error message.
Can any one help me to give the logic please

 

[Joshdbr]

Try using RegularExpessions.