I figured it out, I just need to create my own version of urlcontrol.ascx & also create my own version of fcklinkgallery.aspx to do this. Within urlcontrol I'll just need to change the way that the upload works so it goes into knowledge tree & populate the drop down list from the docs in kt.

Thanks for the pointers on this to date. I've just got started on it again and have managed to basically port both fcklinkgallery.aspx & urlcontrol.ascx to C#. Before I start making any changes to the functionality I wanted to make sure that the code I've ported still works as it did before. I've been through and reviewed all of the code to verify it matches up to the VB equivilent, but when I modify the web config for it to work with the new code I get the following in the event log when I go to the new link browser through the editor:

AssemblyVersion: 04.08.00
PortalID: -1
PortalName:
UserID: -1
UserName:
ActiveTabID: -1
ActiveTabName:
RawURL: /Website/KtEditorFiles/KtLinkBrowser.aspx?FCKTheme=Default&tabid=36
AbsoluteURL: /Website/KtEditorFiles/KtLinkBrowser.aspx
AbsoluteURLReferrer: http://localhost:4054/Website/Providers/HtmlEditorProviders/Fck/FCKeditor/editor/dialog/fck_link.html
UserAgent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8.1.11) Gecko/20071127 Firefox/2.0.0.11
DefaultDataProvider: DotNetNuke.Data.SqlDataProvider, DotNetNuke.SqlDataProvider
ExceptionGUID: 315946c6-6a19-4a94-a682-c771034e9814
InnerException: Object reference not set to an instance of an object.
FileName:
FileLineNumber: 0
FileColumnNumber: 0
Method: DotNetNuke.Services.Localization.Localization.GetEnabledLocales
StackTrace:
Message: DotNetNuke.Services.Exceptions.PageLoadException: Object reference not set to an instance of an object. ---> System.NullReferenceException: Object reference not set to an instance of an object. at DotNetNuke.Services.Localization.Localization.GetEnabledLocales() at DotNetNuke.Framework.PageBase.get_PageCulture() at DotNetNuke.Framework.PageBase.OnInit(EventArgs e) at System.Web.UI.Control.InitRecursive(Control namingContainer) at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) --- End of inner exception stack trace ---
Source:
Server Name: STF-040-LAP01

Any ideas on why this might be happening?

I searched and only really found this error related to IIS 7, but currently I'm working with it through VS05 for development.

Cheers Wayne