you have two choices:
1. You have to check in which format the Date is defined in your Excel (i.e. {mm/dd/yyyy} or {mm.dd.yyyy} etc. ), you can do that by checking the cell format. so if its defined like this mm/dd/yyyy you need to change your date to 01/11/2011.
After you did that and wrote it in the cell, change the cell TYPE to "General".
2. If you want to keep your date in this format {mm.dd.yyyy} as you write it, then you have to change how the date is defined in your excel (again go to cell format and choose the desired templete in our case {mm.dd.yyyy}.
After you did that and wrote it in the cell, change the cell TYPE to "General".
Hope you understand and it works