Yes, we know this already, from Bruce Miles, who writes that Lou Piniella has decided on his rotation:
Lou Piniella did that Monday as he filled in a couple of key blanks. After Carlos Zambrano pitches the April 2 opener against the Reds in Cincinnati, lefty Ted Lilly will go in the second game of the season, two days later.
Jason Marquis will pitch the series finale in Cincinnati, and lefty Rich Hill will open the Milwaukee series on Friday, April 6.
Which means that the fifth starter -- whoever he is, as Piniella says that's still an open question -- will start Saturday in Milwaukee (since Lou says in Miles' article that he won't skip the fifth spot, even with the April 3 off day), then Z will throw the Sunday game at Miller Park, and Lilly should start the home opener against the Astros on April 9.