If you go to
Here, Canon's software download page, it seems there is no software available for the Canon 720IS digital camera. Once selected, it gives an error page.
If the software were available it wouldn't be opened in Outlook, it would be a a file, a zip file or a folder, saved to a destination on your computer's hard drive of your choosing.
I suggest you phone Canon directly or visit a local photography shop and see if they can help you.
I'm assuming you've lost the CD that came with the camera?