Well basically you'll have to code it yourself. This will involve setting the Dock property, e.g. to DockStyle.Left for when the panel is always visible. Then you'd have to control the Width property, probably based on a Timer with various settings to let you know if the mouse was over the control.
Alternatively search for some existing controls which provide this functionality (a quick search revealed PlusDock and Nevron which provide this functionality, or this free script: http://www.codeproject.com/KB/miscct...icdocking.aspx
/- Sam Judson : Wrox Technical Editor -/