Hello Mark,
you need to be more specific with the error messages (a good way
would be to past it somewhere [1] so you can later have a link handy
when you write your email).
Next time I would do this:
- check whether the internet connection is actually working
(open the browser and launch a search)
- if so, type `sudo apt-get update`
- then type `sudo apt-get install mnemosyne`
And finally report back ;) I am sure we can do it
-F
[1] like
http://paste.debian.net/