Are you hard of hearing in your right ear?
I think the strategy I would take with the hearing thing is to try to get in a conversation with just one person at a time. (My husband has a hard time hearing more than one thing at a time, so in a convention or whatever he has the same issue you do. Background noise just does him in.) This gives you the opportunity to really pay attention, and those people will remember you better if they perceive you as someone who really listened.
As for breaking into a group, I don't see anything wrong with waiting for a lull in the conversation and walking right up and sticking your hand out and introducing yourself. It's a networking meeting, after all? Have an icebreaker question to ask. Not something vague like "where did you go to school", but something a little more specific like, "Don't I have a class with you?" or something stupid like that.
Moving on from a convo? Just excuse yourself for a refreshment. Read the clues and get out of there before it gets dead silent.
Karen