Yes - it's straight forward. If the folder is called 'store' you would just upload the entire contents of the PowerStore300 folder to your 'store' folder, navigate to any page in that folder, and the set-up will begin.
I have just done this. The menu structure is entirely intact. Just a link from your existing pages to 'store/' will open the store front page (and therefore all store pages). You would then just need a link from the store pages back to your existing home pages.