Question: I have a form that takes user input and then let the user get connected to the sql server.
This is happening on button click.But where can I set the property Default button so that the user when clicks enter do the work of that button.

Answer: 
It is called `AcceptButton` now on the form; set that to the button that will be the default button.  

Refer to [Form.AcceptButton Property](http://msdn.microsoft.com/en-us/library/system.windows.forms.form.acceptbutton%28v=VS.100%29.aspx)
In addition to Form.AcceptButton property the "OK" button must have the TabOrder property set to 0 and all other controls within the form should have a TabOrder >0.

This can be done using a form resouce contruction kit or by code eg.
buttonOK.TabOrder = 0;