Yeah, moire is a bioch, I have had to retone whole pics coz of moire, so I'm thinking really seriously of making shadows with just plain, solid greys, it probably is the most optimal way for digital comics, cuz when resizing it's kinda impossible not to get some kind of moire, there are ways to minimize it tho. I should advice on following Loomie's advice (the one Reoma posted).
I love tones, but the truth is, when the pic is resized it's pretty difficult to tell what is a solid grey and what is a screentone. Wait, there is, the one with moire is a screentone (I'm just joking).
There was this article back in our inkblazers days, I think the title was: No more moire!, darn I wish I read that and saved it, from what I could tell it had pretty good reviews =S. Sadly I don't know where it went since IB's shutdown.
Anyway, good luck fighting the moire. Fightin' ! oo.oo