hey ... ucsd pal
of course it'll have a little effect, but it also depends on when you got them and what classes they were for.
but if u do hv c's, d's, or f's .. usually it's better if it's 1) towards the beginning, 2) all cluttered in one year or so, 3) if you have retaken the class and got at least a B or better (perferrably an A).. and of course, if you can, really explain to them why u got those grades.
for me, i have gotten 1W (Bio 2), 1C- (bio2), 1C (biochem - 2nd quarter), 1C+ (ochem lab - first one). for me i had an excuse for bio 2 and ochem cuz so much was goin on in personal life. but biochem was totally cuz i cannot accept the prof's style of teaching and testing
but to be able to get to an interview, make ur application shine.
personal statement: catching, conscise, to the point... and importantly clean of grammatic errors. personally i am horrible in grammar so i had a couple friends that i trust read over my personal statement and have them correct it until it's spotless.
have a lot of e.c. activities. work exp, vol exp. everything is a plus to ur applics. don't worry...