I'd like to give a "knit fabric" effect to a cake I will be making for a group of knitters. Do you any suggestions ? Thanks for your help!

I've seen this in some of Colette Peters' books. She does a Father's day Sweater and a Baby bib. To create a "knitted look" she uses a #3 tip to create overlapping rows of small loops. Think of writing a cursive lower case letter "e" over and over again. It looks like a loosely knitted fabric.
Hope that helps.

Here's a tutorial from craftster... http://www.craftster.org/forum/index.php?PHPSESSID=247657b2053c1b05e9033e575f9c2bfd&topic=174630.0