Here are a few links relating to Physics2D.Net.
Erin Catto's Site (The mastermind behind Sequential Impulses.) Game Physics
A 2D Physics Engine for XNA: Farseer Physics Engine
A OO C# Wrapper for SDL (The Library I use for the Demo) SDL.Net
A collection of C# Wrappers of portable Game Libraries. Tao Framework
My Original 2D Physics Engine: Physics 2D
A Game Engine that uses Physics2D.Net Xilon Engine II.Net