flat I-cord in *usually* done on DPNs or a circular because you are always sliding the stitches back, so it goes like this:
k5, sl 4 pwise
turn and slide sts across to other side
carrying working yarn across back of work, k5, sl 4 pwise
turn and slide sts across to other side
repeat, etc.
However, I'm not familiar with making an I-Cord with slipped stitches except when doing an applied I-cord at an edge, so it might be different.... you might just knit normally back and forth, the slipped stitches that you are knitting 5 of the next row creating the applied cord...
These are standard instructions:
http://www.stitchdiva.com/custom.aspx?id=196