Use the knit or cable cast on. You don't have to start with a slip st, just pretend you've already cast on a bunch of sts. Move the needle with the sts on it to your left hand, and knit into the first one (or between the first 2 sts), don't take the st off the left needle, put the new st on the left one and repeat. When you've added 6 sts, move the needle back to your right hand and knit the next section.
sue- knitting heretic