Depends. You can use a circular needle to knit back and forth on a flat piece, or you can join it into a tube and knit around. I've found it much easier to knit large pieces (afghans, f'rex) on a circular needle than on a long pair of straight needles.
You may also want to try casting on using a larger needle than you'll be using for the rest of the piece.
jenn
-- Jenn Ridley : snipped-for-privacy@gmail.com WIP: Poppies (Art-Stitch), two knitted tops, Oriental Butterfly Most recently Finished: Floral Sampler, Insect Sampler