Why take the pain to work on an obselete technology. It was not more than a year that DTD had come and everybody was waiting for XML Schema. And this story belongs to year 1999 !
But for the question, those two lines are not different. Parantheses are for grouping child elements into groups. The second line ( <!ELEMENT Test2 (ItemA, ItemB?, (ItemC)*)> ) has no groups!
System Advance, UK