How do I transfer a site mirror I downloaded to my old computer to my USB drive
to I can transfer it to my new computer? (The site was a blog that's now gone,
so I can't just copy it again.)

When I right-click on any downloaded files on httrack on my old computer, it
just gives me a pop-up box with the name of the file and no option but to
click an "OK" button. 

Thanks for any advice!