If by 'improv[ing] your credentials' you mean raising your gpa, etc., and you have already taken all or most of the prerequisites for school then you might consider an SMP. It's a master's program designed for post-baccalaureate work to improve your gpa and knowledge of the necessary sciences and thus improve your chances of being accepted into the school(s) of your choice.
If you have completed your baccalaureate already, but have none or only a few of the prerequisites completed then you could try a post-baccalaureate program. There are quite a few of them. You could also consider reenrolling in a university nearby and taking the classes on your own, as opposed to a structured program. I am seriously considering a post-baccalaureate program myself currently, so can only speak from my research, not actual experience! I know little, if anything about SMP programs, but you can do a search on the forum or do a little research yourself.
Most of the following is with reference to post-baccalaureate programs, and not SMP's. My info is based on my research and the opinions I've formed from various school websites and others' posts here.
Is it difficult to get accepted to one of these programs? It depends on the program I guess! I have only researched a handful of them, but some are definitely more competitive than others. Many require that you have a minimum of a 3.0 gpa from your undergrad. Some require that you have some research, clinical, and/or volunteer experience. Some also require you to submit letters of recommendation along with one or more essays. Many also require an interview. It's similar to reapplying to school.
This link is a list of both SMP's and post-bacc's:
http://services.aamc.org/postbac/
Here's another:
http://hpap.syr.edu/LISTPB.HTM
Some of the more popular/'prestigious' programs I'm aware of are: Goucher, Bryn Mawr, John Hopkins, Penn, Columbia, Harvard Extension School, Northwestern, Tufts and Georgetown.
I've gotten the impression that Goucher, Bryn Mawr and John Hopkins are some of the most difficult to be accepted to in general. Some of those I've just listed are more economical than others it seems as well. This would include Harvard, Penn, and Northwestern. Another one that it really cheap is Maryland's Science in the Evening program. There are probably a whole list of other schools just as cheap or difficult to be accepted to, but I've not researched them.
One important aspect of each program is to find out what percentage of those who finish their program are accepted into med/dental school. You can check out each program or contact them to find out their acceptance percentages.
Do you get a degree for completing the program? Obviously, if you finish an SMP you will be awarded a master's degree. As for post-bacc programs some offer certificates, but it depends on each program and they also have varying requirements to obtain the certificate. You'll really have to check each program online to get a better feel for it.
How difficult are they? I've heard that they can be very challenging, especially depending on where you go. I am not speaking from experience though, as I've already stated. Many programs have their classes graded on a curve, so it makes it more challenging because you're competing with other bright students, many of whom are in the same shoes as you and are going back to school with perhaps more maturity and motivation.
What classes?
Mostly science courses. If it's a post-bacc for fulfilling your prerequisites you could take Inorganic chemistry 1 & 2, Organic chemistry 1 & 2, Biology 1 & 2, Physics 1 & 2, and maybe even biochemistry, calculus, psychology, or English. It depends on if the program has it's own requirements, what the prereq's are for the different school's you're planning on applying to, how much you need to raise your gpa, etc.
Does it help for applying for med schools? It seems to me that one way it can help, besides the obvious ways it can cover your prereq's and give you an opportunity to get extracurricular under your belt, is that it can show admission committees your dedication due to the fact that you're possibly stopping a career to study medicine. Some have said that this evidence of dedication to healthcare has been a big boost for their application. It can show a lot of personal sacrifice and dedication to one's goals.
I'd recommend looking at each school's site for info on the programs themselves. Also, spend a few hours reading and skimming through these forums. Their is some valuable info here. Try using the search tool as well. Be aware that anyone can post here, so you'll find good and bad info, but it's really up to you to sift through it. Good luck!
