You are in the wrong forum... you need http://forums.adobe.com/community/premiere_elements?view=discussions
PS - you download from an Internet site to your computer, you INSTALL a program on your computer
[Moved to Premiere Elements forum.]
What version is the original purchase Premiere Elements/operating system?
If you purchased online downloaded Premiere Elements Windows, you will have to purchase a serial number for the Mac product.
When you purchase an online download, your purchase is specific to the operating system to which it is download (Windows or Mac). If you had purchased the product in a boxed packaging, you would have two installation disc, one for Windows and one for Mac.
Please contact Adobe Chat for further Adobe confirmation of details