Same way, more or less.
One way is to define an interface that exposes a method that "tip" code will use to communiate with the form. You would then replace the "form" parameter with a parameter of the interface, and call that method. In the form, the method is implemented to populate the text box with the tip message.
Another way is to declare a delegate, and define a method that uses the signature of the delegate on any form that you want to be able to inject a tip message. Then you would pass the delegate to your Display_Tip method and it would callback to that delegate for the message.
Another way is to have the tip code return the message and let the form to the work of populating the textbox.
Another way is to use reflection to find the textbox on the form. The form would have to passed as an object.
Another way is to loop through the controls collection of the passed in form and set the text on the one named txtTips
Another way is to merely pass the textbox control that you want to put the text into instead of the form.
Another way... there are probably at least 100 ways to do this.
Woody Z http://www.learntoprogramnow.com