Here are some links to photos and information on snake species of South Carolina.
How to Identify Snakes
http://www.snakesandfrogs.com/scra/ident/index.htm
Main page of guide to snake species of South Carolina
http://www.snakesandfrogs.com/scra/snakes/scsnake.htm
Seven common small snake species photos
http://www.snakesandfrogs.com/scra/snakes/small_snakes_poster.htm
Photo of baby black rat snake (One good possibility of being the species you saw)
http://www.snakesandfrogs.com/scra/snakes/images/bratjuv4.jpg
Juvenile black rat snake (young, but older than a baby)
http://www.snakesandfrogs.com/scra/snakes/images/blackrat3.jpg
More photos of black rat snake at various ages from baby to adult, as well as information on the species.
http://www.snakesandfrogs.com/scra/snakes/brat.htm
Yellow rat snake baby is another possibility, babies are splotched whereas adults are striped.
http://www.snakesandfrogs.com/scra/snakes/images/yratjuv.jpg
Another possibility, juvenile Eastern Kingsnake
http://www.snakesandfrogs.com/scra/snakes/images/ekjuv1.jpg
Eastern kingsnake info and photos of various ages
http://www.snakesandfrogs.com/scra/snakes/chain.htm
Here's a cool site I found to use for identifying animals of all sorts in North America!
http://www.enature.com/home/
Here's the link to the snake ID section of the site.
http://www.enature.com/fieldguides/view_default.asp?curGroupID=7&shapeID=1060
Incidentally, KINGSNAKES ARE NOT POISONOUS!