This is not exactly the same version number (this is "AssemblyFileVersion", not the "AssemblyVersion" attribute), but you can use the following line of code:
System.Windows.Forms.Application.ProductVersion
Returns a string.
If you are doing automatic assemblies, you need to remember to increase both numbers.
ClickOnce, :
System.Deployment.Application.ApplicationDeployment.CurrentDeployment.CurrentVersion
,