Don't know about manipulating - you can probably make cards using a site like Photobucket or something?
Re: scanning - most printers are scanners these days, maybe someone you know could do it? Otherwise, yes, maybe Staples, or any copier shop. You'd need to bring a USB stick to put the image on, or maybe they'd let you mail it to yourself ...
I am not sure where you could get the picture scanned: this is not generally available as a service. Jessops do a walk-in 35mm negative scanning service (film scanners are more expensive than ordinary flat-bed document scanners, so not many people have one) so they might do it for you.
You would probably get a good result just by taking a photograph though - can you borrow a decent digital camera?
If you are really in Tobermory you need to use an online service like VistaPrint .
If you live on Wimbledon Common though, you could walk in to a local print shop and ask them. You will get a lot more help and advice, and the end results will probably be better because of that, but they will cost more per card than online, and may require a large minimum order.
If you are planning on using a local independent copy shop, go in and ask them. You will probably find they use Macs, although not the same software as you!
When I say you will get a better end result, I don't mean shinier paper, I mean a good local printer should put the effort in to get something that looks good printed. An online service will just print what you send them, and because printing works differently to displaying things on a screen, the end result may not be as satisfactory.