a problem...

[myjoyoverflows]

I'm *trying* to knit these...

http://www.knitty.com/issuesummer06/PATTknucks.html

but I've never knit with three needles in a triangle (I don't know what any special terms for it would be) and I'm doing the stockinette stitch...but, I don't know how to tell where the "row" ends when going back and forth between knitting one row and purling the other....help? I'm not sure how to tell where to stop knitting and where to begin purling...am I making sense???