knitting question

[nancy619.livejournal.com]

I recently taught myself to knit and feel pretty confident on your basic knit stitch. I would like to make a scarf with vertical stripes. How is this done? I've seen a lot sites saying that you knit the scarf length-wise on circular needles. Right now I only know how to use straight needles and obviously a scarf is too long to knit lengthwise on straight needles.

Help!