HWND ToolBar(HWND hWndParent, HINSTANCE hInst){

	HWND				hwndTB; 
	TBADDBITMAP			tbab; 
	TBBUTTON			TB_Button[6]; 
	INITCOMMONCONTROLSEX	icex;
	int				num_of_Buttons = 6,i;

	icex.dwSize = sizeof(INITCOMMONCONTROLSEX);
	icex.dwICC  = ICC_BAR_CLASSES;
	InitCommonControlsEx(&icex);

	tbab.hInst = hInst;
	tbab.nID = IDR_TOOLBAR1;

	hwndTB = CreateWindowEx(0, TOOLBARCLASSNAME, (LPSTR) NULL, WS_CHILD | WS_VISIBLE, 0, 0, 0, 0, hWndParent, (HMENU)NULL, NULL, NULL); 
	SendMessage(hwndTB, TB_SETBUTTONSIZE, 0, (LPARAM) MAKELONG (30, 30));
	SendMessage(hwndTB, TB_BUTTONSTRUCTSIZE, (WPARAM) sizeof(TBBUTTON), 0);

	SendMessage(hwndTB, TB_ADDBITMAP, (WPARAM)num_of_Buttons, (LPARAM) &tbab);
	SendMessage(hwndTB, TB_LOADIMAGES, IDR_TOOLBAR1, (LPARAM) hInst);
	ZeroMemory(&TB_Button, sizeof(TBBUTTON)*num_of_Buttons);

	for(i=0; i < num_of_Buttons; i++){
		TB_Button[i].fsState = TBSTATE_ENABLED; 
		TB_Button[i].fsStyle = TBSTYLE_BUTTON;
		TB_Button[i].iString = 0;
	}

	TB_Button[0].iBitmap = 0;
	TB_Button[0].idCommand = BUTTON_0; 
 	TB_Button[1].iBitmap = 1; 
	TB_Button[1].idCommand = BUTTON_1; 
	TB_Button[2].iBitmap = 2;
	TB_Button[2].idCommand = BUTTON_2; 
	TB_Button[3].iBitmap = 3; 
	TB_Button[3].idCommand = BUTTON_3; 
	TB_Button[4].iBitmap = 4; 
	TB_Button[4].idCommand = BUTTON_4; 
	TB_Button[5].iBitmap = 5; 
	TB_Button[5].idCommand = BUTTON_5; 

	SendMessage(hwndTB, TB_ADDBUTTONS, num_of_Buttons, (LPARAM) (LPTBBUTTON) &TB_Button); 
	SendMessage(hwndTB, TB_AUTOSIZE, 0, 0); 					
	ShowWindow(hwndTB, SW_SHOW); 
	return hwndTB;
}

Weiß jemand Rat, was mache ich falsch?

Microsoft Windows assumes that all of a toolbar's bitmapped images are the same size. You specify the size when you create the toolbar by using CreateToolbarEx. If you use the CreateWindowEx function to create a toolbar, the size of the images is set to the default dimensions of 16 by 15 pixels. You can use the TB_SETBITMAPSIZE message to change the dimensions of the bitmapped images, but you must do so before adding any images to the internal list.

schon probiert?
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/shellcc/platform/commctls/toolbar/messages/tb_setbitmapsize.asp