Hmm, it's highly unlikely that you're using an HTTP proxy unless you configured one yourself, or you're connecting through someone else's network (workplace, university, etc). Leaving it blank is the normal thing to do.
I'm not sure what's going on with your connection. Normally with broadband (ADSL) the connection is "always on". Are you sure you've got broadband (ie: can you use the phone and the internet simultaneously?) If you're actually connecting to dialup I'm not sure how you could do that on the minimal install, as I've never used dialup on Ubuntu.
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