put ristrictions on a field

the field contains data such as...... 21.10.2012 or 11.11.2012.

it is a text field.so i want to ristrict a user with the following conditions:

1)after first two digits there should be a point "."
2)after 3rd and fourth there should be a point "."
3)only contains numeric values.

for this i want to use CONTROL to ristrict the user.
i cant use date format here

plz help.....

thanks,
pulkit​

 

pl. enlighten why you cant use date format. whats the idea ? bcoz using date field take cares all your requirement.

 

i cant use date format here because the UDF is string type which which already contains alot of data.so i cant change the UDF and thus cant use date format.