Hi, Don't panic, we are nearly there but I know how frustrating these things can be.
When you click "choose source and destination panels", then next page opens showing two separate panels, both of which should show the different directories you have connected, i.e. C:\ H/D , possibly D:\ Disc Drive and possibly E:| external H/D, it also shows the clusters, etc of each.
I assume the external hard drive is plugged in?
In top panel, Click on the actual E:\ line which is where the wanted files are (source drive?) and leave it highlighted.
Now i bottom panel click on the C:\ line which is where you want to store the rescued files (destination drive?) and leave it highlighted,
Now click "choose directory" button which opens another panel and choose the folder in that panel where you wish to store the rescued files.
See how you go and keep in touch.
Wak.