Need advice on "investment banking" position

A little background about myself first:
I graduated from St. John's University in 2010 with a Finance degree. I went off course and tried pursuing something with automotives but decided against it after some time. So I'm basically starting as what you could consider a late bloomer of a college graduate (no real career-related experience). I did some temp. work at KPMG recently but that ended in March. I want to pursue a career in Finance, and I know I'm not as desirable considering I've graduated a while ago, not from a top tier college, nor did I have a magnificent GPA.

I applied for an internship position on a web posting for an investment banking firm. I spoke with the MD on the phone about the position and he stated it'll be a full time position for me, instead of an internship, since I'm out of college. Salary is 100% commission based, which worries me. It appears to be heavily based on making deals with loans for the most part. I'd play a large part of the deals from start to finish, which looks enticing for experience. The problem I see is that this appears to not be the normal IB job I hear about where it's usually salary based, and working heavily with excel. The job application just seemed to easy and simple, like they are willing to give anyone a chance. I received an email directly from the MD about when I could talk no more than an hour after applying. I haven't gotten the position just yet as I've still got to still come into the office for face to face interview. I'm just looking for some insight on this type of position if anyone has experience or knowledge on it. Not to down myself, but I know IB jobs are reserved for the best and brightest minds. I did check the website and googled about it and it appears to be legitimate. There are 8-10 employees to my knowledge. The position, to me, sounds like I'll be doing a lot of cold-emailing (maybe cold calls, aswell) like a telemarketer or insurance salesman, but for investing. Also, dealing with the possibility of not coming home with a paycheck for a month, or possibly longer is hard to swallow. Thanks.