If you have the professional version of 2012 you can use the following link.
http://msdn.microsoft.com/en-us/library/aa942846(v=vs.110).aspx
Essentially you will need to add a User Control (this becomes your custom task pane)
If you are using express edition of Visual Studio it would be ideal to download and use NetOffice - http://netoffice.codeplex.com/
The following is an example of the code I have used in my project. I have added a user control called UserControl1. This is using the Ultimate version however it is the same for at least the professional version.
Private myUserControl1 As UserControl1
Private myCustomTaskPane As Microsoft.Office.Tools.CustomTaskPane
Private Sub ThisAddIn_Startup() Handles Me.Startup
myUserControl1 = New UserControl1
myCustomTaskPane = Me.CustomTaskPanes.Add(myUserControl1, "Picture Table Editor Pane")
With myCustomTaskPane
.DockPosition = Microsoft.Office.Core.MsoCTPDockPosition.msoCTPDockPositionFloating
.Width = 300
.Height = 400
.DockPosition = Microsoft.Office.Core.MsoCTPDockPosition.msoCTPDockPositionLeft
.Width = 300
End With
End Sub