I'm not 100% sure what you mean by your question. This upcoming match is for positions to start July 2007. It's unclear by your description if you are finishing med school in September 2006 or September 2007 (although by your wording I expect it's the latter)
#1 -- If you plan on graduating in September 2007:
If you were a student in an allopathic program, you would not be able to participate in the match at all. The relevant section from the User Guide from the NRMP website is as follows:
For a senior in a U.S. allopathic medical school to participate in the National Resident Matching Program (NRMP) as a U.S. senior, the following requirements must be met:
the applicant has attended a U.S. medical school accredited by the Liaison Committee on Medical Education (LCME)
the applicant has been determined to be on schedule for graduation in the year of the Match and to be eligible to enter graduate medical education by July 1st by the schools dean of student affairs. (Page 5 of the PDF, page is numbered #3 at the bottom)
Because you are a DO applicant, the NRMP considers you an independent applicant and hence you are not held to the above rules. However, you are held to the match participation agreement. If your matched program requires that you start on July 1st (which all will), then I am pretty sure that if you can't be there on July 1st, you could be considered a match violator. The same situation develops for IMG's who run into visa problems -- if you can't start on July 1st (even if it isn't your "fault"), the program could petition the NRMP for a waiver of the match commitment, theoretically give your spot to someone else, and could consider registering you as a match violator.
Hopefully, any PD who is paying attention will notice your graduation date after July 1st 2007 and will realize there is a problem, but I think you need to be 100% up front about this, as you could end up in big trouble.
#2 - You graduate in September 2006
If you are off cycle and are graduating in Sept 2006, then all of the above is moot. Instead, you can now apply through the match, but could also accept a position outside the match instead. Programs could start you off cycle -- i.e. you could actually start training in January 2007 if they have a spot open. If you do accept a spot outside the match, you must withdraw from the match.
