(This topic popped up again today - so I'll post a reply in case others are looking for ideas besides the original poster)
If you have access to both ArcGIS and the Spatial Analyst Extension, there are a variety of processes available. Here's some topics to look at to help you get started:
Overview of Hydrology Toolset
ArcGIS Help 10.1
Understanding Drainage Systems
ArcGIS Help 10.1
Hydrologic Analysis Sample Applications
ArcGIS Help 10.1
Deriving Runoff Characteristics
ArcGIS Help 10.1
Chris Donohue, GISP
