don't know which Microsoft Office software to purchase

I need help. I m not the smartest when it comes to computer. I'm needing to add Word, Powerpoint and Outlook to my inspiron B130. I'm looking at purchasing Mircosoft Office standard. What's the different, (beside the price :smileysurprised:) from the upgraded one and the not upgraded. Which one do I need to purchase?

Thanks

Carla Jane