The interview process is fairly straightforward:
Phone Call: Be yourself, more than anything this is to make sure you don't sound like a child/badger. Cheerful, happy, enthusiastic.
Group Interview/Presentation: Don't worry about anybody else in the room. If they had a single thing going for them they wouldn't be interviewing at Loopnet. You're in for an entry level sales gig, that's it. Nobody has a single thing going for them.
Final Interview: They'll interview you in a 1-2-2-1-1 format. Basically they're seeing how you handle stressful situations and they're looking for someone who can close. Close them, walk with the job. No big deal.