Background:
I worked a lot with C#.Net in the last years (Visual Studio).
At the moment I am on a project for iPhones, I use the iTunes MobileDevice.dll and have a lot of reference code in C.
I try to give my best to do it in C#.Net but I give up now and like to change to C.
So I will now rebuild my C#.Net Code, its a WinForm Project with a lots of events and so on.
Now I search the best IDE, I tried Eclipse but as far as I see there is no WinForm Visual-thing I can use, or? Ideas?
There is no such thing as WinForms for C, nothing even close as far as I know.
However, C++/CLI might be what you are looking for. Because it is c++ it can easily interoperate with C libraries, and because it is also .Net is can interoperate with .Net libraries (like those that comprise WinForms).
Some other Stackoverflow questions have addressed this and their answers are informative:
How to use C++/CLI to program Winforms applications
Can I use C++/CLI (.NET Winforms/WPF ) to provide GUI for app written in native C & C++
If you go the C++/CLI route, Visual Studio will likely be the best visual IDE.