Student changing course (MA-->PGDip)...immigration issues

I'm a non-visa national currently studying an MA in the UK, and I hold a valid student visa which expires on 31 October 2007. But with the recent expansion of SEGS (now IGS) eligibility to students studying Postgraduate Diplomas I'm seriously considering switching onto the PGDip track instead of the MA track for my subject (the way it works at my uni is that you can just do the taught portion of the MA course and get a Postgraduate Diploma...you have to do the dissertation to get the MA, but that's the only difference between the two programs.) The main reason for doing this is so I can finish my studies at an earlier date (June as opposed to January) and thus apply for IGS earlier (and thus, be in full time employment earlier.)

However, I don't know how changing course (in the same subject area mind you just slightly different level) impacts my student visa- I have valid leave as a student until October so I was kind of assuming that switching to PGDip wouldn't be a problem and I could stay the full length of the visa and work after my course is over (I know I can't be self-employed or fill a permanent full time vacancy while on a student visa, so I'm thinking just doing short-term contract work over the summer until I get IGS.)

So, my question- does the Home Office have to be notified if I decide to go this route? Would I have to get a new student visa or can I just finish out the leave on this one? Any insight would be appreciated.