Populate a text field with the subtype description

[DeanFletcher]

Using: Arcinfo 9.3.1 with  Model builder and GP Models.

Have: A featureclass that contains a subtype.
          Using Models  have added a new text field to hold the subtype description.

Need: To use 'Calculate Feld' tool with some pyton code to to populate the field with actual subtype description.

Is this possible to do with the 'Calculate Feld' tool ?

Thanks