I seriously believe that with interviews, in the end you've gotta be yourself. Maybe it's not such an issue at our level (or at least, the general age of BOSsers), but if you act too much, or fake your resume, you generate all sorts of expectations which don't you would need to act to fulfil. From there, If you've got to act to be the type of person that the employers are looking for, for that job, I'd personally question (but not necessarily rule out) the fact you might even want the job, in the long run... That said, its easy to be nervous and in turn, it's difficult to be yourself... I'm sure we've all had the pre-interview-jitters.
Group interviews: generally only done for pretty average jobs... so, what're the good things in lowish, "pretty average" jobs? --
Good communication, teamwork, leadership with appropriate cooperation, acknowledgement of others' good ideas is a good move, too... Listen to what people have to say, even if it seems entirely stupid...
Just make sure you are generally outgoing and happy and you'll be fine.