In her book The Herbal Kitchen, Kami McBride gives quite a few recipes for herbal sprinkles and using powdered herbs in honey, butters and other culinary uses. You can purchase powdered herbs or make your own.
Step 1: Dry Your Herbs
Step 2: Crushing into a Powder
This can be achieved by several methods and can also depend on the type of herb you are crushing. A quick note here, the more an herb is handled, crushed and powdered the quicker it will break down and loose potency. Because of this I always store my herbs in as whole of form as possible and then powder right before using. My preferred method of powdering is in my high powered blender (Blentec) for large amounts and a simple coffee grinder for smaller amounts. You could try a regular blender but they just don't have enough power to turn anything into a powder. Another option is with mortar and pestle, many people swear by these for crushing their herbs but personally I find it time consuming and the results weren't any better than my coffee grinder. After powdering the herbs shake through a strainer to remove larger particles that didn't get powdered.
Step 3: Storage
If I am making an herbal sprinkle I just use old spice jar containers or some really cool jars I pick up when I am out and about. You can also purchase empty spice containers and I always suggest glass which will keep your herb potent longer and keeps the flavor bold. Try to store in a cool, dark place for a longer shelf life. Label with the date you powdered the herb and what it is. Once your powder loses it color and aroma it is no longer medicinal and time to discard into the compost pile.
Powdering Roots & Bark
When making an herbal powder from a root, make sure to wash thoroughly to remove all dirt and debris. Chop the root while it is fresh and then dry the chopped pieces in a dehydrator. Blend the root pieces in a coffee grinder or high powered blender. If you want a real fine root powder you need to purchase your roots in powdered form from a good quality herb store like Mountain Rose Herbs or Bulk Herb Store. The commercial grinders they use to powder the herb is the only way to get that smooth, fine powdery texture out of a root.