If you go back into Synaptic, do both the eagle packages indicate they are installed?
If so, if you go back to your first link, click here there is a crucial piece of information at step 7, relating to going to a "root terminal". Did you do that? (essentially in Linux, only "root" - administrator in Linux can make configuration changes). Further, please understand unlike Windows, virtually ALL commands are case sensitive, so must be copied with great care.
When you got to step 8, did "eagleconfig" work, and did it tell you the configuration was successful? (step 14)
To be honest, you've jumped in at the deep end, not through any fault of your own, but getting modems to work in Linux can be a nightmare.
The easy option is to buy a ADSL/Router, but I appreciate if you are only trying the system, you may not want that expense.