here's a question though - how do i add in the contrasting color after the 8 or 9 rows of black?Well, I just sort of start knitting with the new color. So when I come to the black stitch that needs a green stitch on top of it, I stick my needle in as if to knit, but loop some green yarn over the top instead of looping black yarn, and pull it through. Then, I weave in the end through the wrong side of the work. Also, when you come to the boundary between two yarn colors, you should "twist" the yarns together, meaning that you just wrap one yarn ball over the other before you start knitting again, so that the two strands are locked together.
I made this diagram:
(ugh, sorry it's smooshed. Click here to see a bigger version.
I tried to number each section in the order that you'd start that mini-ball of yarn, although I didn't really take in to account the direction of the rows. So you start with Ball 1 for a few rows, then on row 9 you add ball 2 for one stitch, then start ball 3 (same color as ball 1, but different section of the pattern), switch to green with Ball 4, then back to black with ball 5, and so on.
On row 14, for example, you'll knit with the strand from Ball 1, then drop it and knit with the strand from ball 2, then Ball 3, then 7, then 6, then 4, then 5. If there's just a few stitches of one color in the middle of another, you can just use one strand for a few stitches without having to start and stop another ball.
KnittingHelp.com has a video about intarsia - I haven't watched it yet, but I'm sure it's excellent.
You might want to start with a smaller intarsia project first, until you get the hang of visualizing the different blocks of color. (of course, I can't really FIND any patterns right now! gah.)