How are you purchasing the software: perpetual license? standalone or Suite? boxed or download? Adobe Cloud subscription?
Premiere Pro is often used in conjunction with After Effects and Audition.
If they will be part of your workflow too, you may be better off getting either Production Premium CS6 or joining the Creative Cloud (for a monthly fee).
http://www.adobe.com/products/creativecloud/buying-guide.html
Selecting Mac or PC (Windows) version when buying online is easily done at the point of sale by selecting the relevant option from the dropdown menu.