I'm using VS 2008 (sp1) (of course it runs on .NET Framework 3.5)
I downloaded FCKEditor.NET 2.6.3 and FCKEditor 2.6.3 (and FCKEditor 126.96.36.199)
I tried add .dll file to bin folder of solution and put fckeditor at root folder (I've tested with both of 2.6.3 and 2.6.4).
Result that I can drag and drog a FCKEditor control to my .aspx page. It displayed well on IE 7 and FIrefox 3.5 .
<FCKeditorV2:FCKeditor ID="FCKeditor1" runat="server" BasePath="~/fckeditor/"> </FCKeditorV2:FCKeditor>