I was able to open that file but it is only available as a download.
It's description is :
application/octet-stream (11.8 KB)
You could consider a disto upgrade to your current OS. The current version of Linux Mint I think is 12 or 13-
I tried Linux Mint 12 KDE recently and it's very nice.
When I did an update a few weeks ago I too got "failed to fetch" I realized it was because my sources.list was a mess and cleaned it up. I was than able to obtain all the packages I needed.
Hope this helps-