If all of your data elements in that field will always be four characters you could simply use the LEFT and RIGHT functions and concatenate the results with a '.' in between. If the length or number of characters will vary then you will need to use the LEN function as well.
LEFT(myfield,2) + '.' + RIGHT(myfield,2)
- or -
LEFT(myfield, LEN(myfield) -2) + '.' + RIGHT(myfield,2)
~Michael
Michael Weiss