ASP.Net Webpart vs SharePoint webpart

Web Parts and Web Part pages were introduced in a previous version of Windows SharePoint Services. In the previous versions, Web Parts were implemented as specific SharePoint-based classes. However, ASP.NET 2.0 includes a Web Part framework that provides Web Part page controls and a more generic, flexible implementation of Web Part classes. Windows SharePoint Services 3.0 uses the new Web Part framework. For example, you can develop a class that inherits from System.Web.UI.WebControls.WebPart and you can then use that class as a Web Part in SharePoint-based sites. Windows SharePoint Services pages include the ASP.NET 2.0 Web Part management controls so that users can add, remove, or modify the properties of ASP.NET Web Parts in a manner that is consistent with non-SharePoint Web Part pages.

When you develop new Web Parts, you should use the ASP.NET 2.0 classes as the start point for your development. However, Windows SharePoint Services 3.0 provides a very high degree of backward-compatibility with previous versions. If you have already developed Web Parts based on the previous version of Windows SharePoint Services, those Web Parts can still be used in Windows SharePoint Services 3.0 sites. For example, if you have developed a Web Part based on the Microsoft.SharePoint.WebPartPages.WebPart , you can still use it in Windows SharePoint Services 3.0 sites.