Flying Fish uses chestnuts in their Exit 8 Brew.
I emailed the brewery asking them how they used them. Here is the response I got.
Chestnut flour in the mash and boiled whole chestnuts (no shell) for the first 30 minutes.
Read some of the recipes in the recipe database http://www.homebrewtalk.com/f73/
to get a good idea of the grain bill for a dark Belgian. Basically they are mostly pils, and then maybe some caramunich, and Special B. Use some D-180 or D-90 syrup to give color and flavor. Get the BU:GU ratio to about .29.
For yeast I like 3787 followed closely by 1214. Both very good yeasts.