Cool, I was looking for a small popup snippet for a webpage and then I found this control:
Introduction
This article describes Asp.Net popup control. This control imitates MSN Messenger alert, but it is designed for using in a web page. Graphical appearance of this control can be completely changed by using one of predefined styles or by modifying all colors used on control.
Very important feature of this control is, that it can be used on most of current browsers. It is tested with latest version of Mozilla, Internet Explorer and Opera. Look of control is different on browsers, that doesn't support filters (filters are supported only in newer versions of MSIE). You can also use HTML in lot of control properties, so you can get popup with icon or anything you want.