Do we have nay .NET framework classes to replace the following API calls?

CreateWindowEx
GetWindowText
ShowWindow
SendMessage
GetWindowRect

Basically we have migrated our application from VB6 to .NET and used same API calls in .NET as well.

Now the time has come to replace all API calls to .NET framework classes.

We used those API calls to validate textboxes by popping up a temporary error message box next to textbox object. After few seconds, the error message box disappears by itself or on loosing the focus of textbox.

If we can use the similar functionality of .NET, then there will be less code changes, otherwise please suggest other alternatives.

Regards