The version you have from a coverdisc is probably in the tar.gz format (or tar.bz2), and you will need to install it that way. However, you will probably run into some dependency problems (gdk files, I would expect, that won't be present in the default Mepis since KDE is the default desktop.) That is why apt-get is the preferable way to get it installed at that would take care of all the dependencies. However, that, I believe, is about a 400mb download and at your connections speed that is prohibative.
You can try to install it from the disk, but you will have to do it from a command line from runlevel 3 (I don't believe you can install it while X is running). If you do get stalled because of failed dependencies, make a note of what they are, and check if they are on the disk as well (Linux Format is pretty good at including many of the dependencies for major installations like Gnome.)
If you get stuck, post here for help.
Hope this helps,