Since this is a topic that seems to come up over and over and over in KAL's I participate in, I thought I'd just blog and link instead of repeating myself. ;o)
Knitting isn't handed.
It simply isn't. You use both hands to knit, just as you do to drive. There are different actions for each hand as you drive (the turn signals are usually on the left, the gear shift on the right, etc.), but nobody talks about left-handed drivers or right-handed drivers, or left- and right-handed cars.
Mystique swirls maddeningly around lefties learning to knit, and thickens the further back you go in time. One lovely lefty lady at my old LYS, Rachel, was taught to knit standing in front of a mirror. Her instructor (a Righty) insisted it would be easier for her to learn that way. But it's really not necessary. If anything, Lefties have an edge in learning to knit, because as has been pointed out more than once: in Continental knitting the left had does more than the right. Elizabeth Zimmerman even called Continental Left-handed Knitting. Check out how I (a definite Lefty) knit: