question of c#

Hello,
Hi!.I have got a problem in calling a method from a Dll
file(user32) using c# like;

[DllImport("user32")]
public static extern /* problem is here*/ GetCapture();

this method return a reference of type "window" which is defined
in the Dll file so i cannot call any method with out the class
avaliable. I used the following syntax and again got error.

[DllImport("user32")]
public static extern object GetCapture();

Exception was thrown :
************************************
System.Runtime.InteropServices.MarshalDirectiveException: PInvoke restriction: c
an not return variants.
at Glass2k.Glass2k.GetCapture()
at Glass2k.Glass2k.handler(Object sender, EventArgs e) in e:\operation badar\
c#\practice\glass2k\glass2k.cs:line 96
*************************************

Can any one tell me how to create a class or interface to
alias or define a class which can hold reference to class type
of windows. Thanks.