I'm not sure what are you trying to achieve but you can's use windows forms in an web application (that's for sure)!
Even if you will be able to Reference the library and write something like this:
protected void btnClick_Click(object sender, EventArgs e)
{
System.Windows.Forms.Form f = new System.Windows.Forms.Form();
f.Show();
}
still you will achieve nothing except a rise in a memory consumption from IIS.
Cheers