haha I'll be doing this costume later at Anime 0asis 2010!
well all the Miku cosplayers I've talked to have either 1. ordered their wig pre-styled with detachable twintails or 2. done what the above posts say
either way would work, but the first option would be a bit more pricey, I'm guessing.
as for the pleated skit, try this:
I know you're going to have lots of fun as miku! She's a really awesome character =3