Hey ivey, i was in your position two years ago. i had 3 C's and an F!! But I wised up after college and took 20 hours of upper-division science classes and got all A's...got a recommend letter from my school's pre-med committee and things are working out now, i'm interviewing and looks like things are a-go this fall. anyway, just telling you that it's never too late to spice up your record even if you did mess up a little as an undergrad...just hang in there, ivey, make sure your post-bacc work is good. also, about taking courses over, check with your advisor but i'm pretty sure both grades will count, in other words if you get a C and then an A, it'll be like a B in their eyes. Might be just as good or better to take whole new courses....
see you and good luck!!!