hmmm...
i say try eating some grass. that always helps me. OH wait a sec, this isn't the premed farting thread...sorry.
since i'm here, let me add a voice from a dawg who's been in public health for several years. i think in general, you should consider your career goals very carefully before you choose which public health track you want to go down - in case med school doesn't work out.
the MPH is an ok degree on it's own and a great companion degree to an MD/DO. however, i don't think you need an MPH to go into public health. in fact i know you don't. so if that's a concern, don't worry about it. the vast majority of people in public health do not have MPHs.
in my experience, this is especially true of the line you're talking about, health promotion/disease prevention. it's also true of health ed and community health ed.
although a lot of my colleagues would deny me my water bowl for a week if they heard me say this, i honestly don't think you need the degree if you're headed for one of those fields. a graduate degree in social work, social psych, ed, health admin or a host of others will serve you just as well. spending a few years at a CBO with some supervisorial experience will do you just as well too.
now if you're interested in epi/biostats, env health, infectious disease, international health or something along those lines, then by all means do the MPH. it will really make a difference. and you will be able to jump into community health or disease prevention, etc. if you want to - not so the other way around, unfortunately.
there are also some fields like maternal and child health where you can get an epi specialization and cross into both community health and HPDP. IMHO, that's a good mix.
finally, you should consider a peripheral field like health services research or bioinformatics or even information technology with a specialization in health information systems. these are all up and coming disciplines. i predict holders of these degrees will be coveted in years to come.
hope this helps. good luck.