[SOLVED] Thanks for all the help.
CaretPos has nothing to do with it, which is misleading.
To drag and drop text from a TreeView node into a RichMemo;
procedure TForm1.RichMemo1DragDrop(Sender, Source: TObject; X, Y: Integer);
var
iNode : String;
begin
inode := TTreeview(Source).Selected.Text; //Treeview is the Source.
RichMemo1.SelStart:=RichMemo1.CharAtPos(X,Y);
RichMemo1.SelText:=iNode;
end;