Is there a designer for SharePoint 2007 WebParts in Visual Studio? I downloaded Visual Studio 2010, and see there is one for SharePoint 2010... but right now we are writing parts for 2007. Alternatively, what is the overhead for using the ASP.NET developer, and porting the results to a SharePoint WebPart?
Since SharePoint 2007 was released before VS 2010 and 2008 (captain obvious over here), they released WSS VS Extensions for creating webparts and workflows in VS 2005. With this setup, you need to be developing in a MOSS environment, since the libraries will expect to be fetched on the server. I use VS2005 with the WSS extensions since its supported by Microsoft, but there are third party templates for 2008 and possibly 2010.
So to answer your question, if you are going to develop in MOSS 2007, i'd use VS2005 with WSS extensions.
What you could do is use the same trick as VS 2010 does for SharePoint 2010.
In VS 2010, there is no real visual designer for Web parts, but a Web part is built out of a user control and of course VS has had a visual designer for user controls for a long time.
Look at MSDN magazine. This article describes the code for a "Visual" Web part and includes the code that the Web part uses to load the user control (figure 5).