Working with sharepoint and ASP.Net 2.0 at the same time I had to know what way we go with the webparts. Well, good news: You write an ASP.NET 2.0 WebPart - it _is_ a Sharepoint 2007 WebPart But dont forget, webparts on Sharepoint 2003 is a different animal!!

http://blah.winsmarts.com/2006/05/19/writing-custom-editors-for-sharepoint-2007-and-aspnet-20-webparts.aspx

http://blogs.msdn.com/mikefitz/archive/2005/03/17/397775.aspx

Getting started with sharepoint webparts?
http://www.intranetjournal.com/sharepoint/
http://www.osix.net/modules/article/?id=660
http://www.devx.com/dotnet/Article/17518/0#codeitemarea

ASP.Net 2.0
http://msdn.microsoft.com/msdnmag/issues/05/09/WebParts/default.aspx