Custom Message Box display, Having some trouble! Options

[Genten]

Hello! A friend and I are currently working on a game, and a feature we'd like to add is a custom message box that displays when you receive an item. Here's a mock-up of something that we're trying to get, made in MSPaint:

[Show/Hide] Mock Up

Obviously, the message would be more centered in the screen. However, we don't know how to do this! Ranchinggal has been trying it out for quite some time and can't get it to work. I know an event similar to this is possible, as I've seen it appear in another RPGMaker 2003 game I've played, but we can't seem to reproduce the effect! We're at a loss, does anyone have any advice? Thank you very much!