After you decide to take the adventure of localizing a WinForms application, you should at first search for helpers, especially the free ones.
For me, the pains of translating is less than the pains with Visual Studio 2005 IDE. In order to reduce your pains, I suggest you install the following tools.
First, Resource Refactoring Tool from Microsoft.
Second, download a tool named ResEx
The first one helps you to extract a hard coded string to a resource string in an RESX file. The second helps you to translate RESX files.
I will go on to translate my project. If I dig something new, I will soon post it here.
[Updated: Now there are even more tools available, such as http://visualstudiogallery.msdn.microsoft.com/3b64e04c-e8de-4b97-8358-06c73a97cc68]