Presumably they are not dates with different formats (in excel)

As the poster mentions the dd/mm/yyyy in the question, they obviously know  
the
Excel custom format feature :)

So I'll assume the various examples have been entered and need turning  
into dates
Can't see any easy way, each different type needs to be split putting day,  
month and year into 3 helper columns.
Try using string splits for 15.03.08 and 2001.04.30
In certain cases those last 2 formats can be converted using "Date -> Text  
to Columns" and using the Date option

You'll need a lookup to convert March, Feb etc into a Month number - for  
the =date()
Then resconstruct the excel data from these, using Date(year,month,day)
This last cell can then be formatted dd/mm/yyyy

Steve