I dont know why people say is so hard. If you have experience coding isnt too much a problem to do anything need to do.
The one I have running on Pioneerz is fully modded with catalog generator and affiliate system and more into it so makes a bit simpler I guess. It has a HTML editor too which the out-of-the-box oscommerce doesnt, you have to know at least basic tags to fancy up your listings.
If need help buzz me or email me and Ill be glad to give you pointers, in the meantime start reading that huge manual, it will help