Quote Originally Posted by Luuk van Venrooij
commctrl is a different unit then ComCtrls. commctrl has al the winapi functions for extended controls. It has TabCtrl_xxxxxxxx fucntions and procedures but not the TabCtrl_InsertItem.
Ahh, this was about CommCtrl unit, sorry.

In any case, I looked at Delphi 6 sources and it seems that Delphi doesn't include TabCtrl_InsertItem at all (neither in Windows unit nor in CommCtrl). Try to use this implementation (pasted from FPC Windows unit) :

[pascal]
function TabCtrl_InsertItem(hwnd:HWND;iItem : longint;var item : TC_ITEM) : LRESULT;
begin
TabCtrl_InsertItem:=SendMessage(hwnd,TCM_INSERTITE M,WPARAM(iItem),LPARAM(@item));
end;
[/pascal]