Will I need to purchase different pistons for my VT V6 Ecotec for converting it in to a Supercharge one and what is the estimate for a conversion?

Unless you're budgeting for a full engine reconditioning, I would highly recommend that you get a good complete L67 engine, instead of upgrading the specifications of your ecotec to that of a factory supercharged 6 engine. Otherwise if can give us a budget to work with then we can help advise accordingly.