Stefani:You can start with the below code from the following thread:http://forums.arcgis.com/threads/20158-Creating-a-multipolygon-polygonYou would need to pass in the polygons from your existing shapefile instead of building the polygons from scratch. That would require a loop through the shapefile where you extract the shape of each polygon.
import arcpy
# Create an Array object for the multi-part feature.
array = arcpy.Array()
# List of lists of coordinates.
partList = [['1.0;1.0','1.0;10.0','10.0;10.0','10.0;1.0'],
['20.0;20.0','20.0;30.0','30.0;30.0','30.0;20.0'],
['-20.0;-20.0','-20.0;-30.0','-30.0;-30.0','-30.0;-20.0']]
# For each part, create a sub-array and populate it with
# point objects
for coordList in partList:
# Create an Array object for each part.
sub_array = arcpy.Array()
# For each coordinate set, create a point object and add the x- and
# y-coordinates to the point object, then add the point object
# to the array object.
for coordPair in coordList:
x, y = coordPair.split(";")
pnt = arcpy.Point(x,y)
sub_array.add(pnt)
# Add in the first point of the array again to close the polygon boundary
sub_array.add(sub_array.getObject(0))
# Add the sub-array to the main array
array.add(sub_array)
# Create a multi-part polygon geometry object using the array object
multiPartPolygon = arcpy.Polygon(array)
# Use the geometry object to create a feature class
arcpy.CopyFeatures_management(multiPartPolygon, "c:/temp/geomTest.shp")