To do it with code you need to do some COM interop.
First, right-click References... -> Add new Reference to Microsoft.mshtml.
Then at the top
Then it's pretty simple
Code:
HTMLDocument doc = webBrowser1.Document as HTMLDocument;
doc.all.item("name", 0).value = "heres the text";
doc.all.item("name of the element", 0).name_of_property_of_element = value;
You should be able to figure it out from there.
The value returned from doc.all.item is a dynamic (in 4.0 or later), so its properties are evaluated at runtime.