Sorry it took me so long to get back with you. I had to get back into the office to look at the parts break downs.
The big differences will be the following. The 03 model had larger front and rear tires, higher ground speed, improved jackshaft bearings at the back of the deck, UltraCut deck (vs. Tri-vantage), front caster wheel bearings, spindle bearings, deck struts, hydro reservoir, mule drive belt, electric clutch (03 was improved), higher fuel capacity, air filter, and possibly deck pulleys. I'm sure there are several other items however that should give you a general idea of the differences.