You can overclock with the H67 chipset if the mainboard you have has the correct settings. The overclock will be severely limited though -- you cannot get 4.5GHz.
The limit for overclocking on the H67 chipset is +400MHz Turbo. With a 2500K, the standard maximum Turbo speed is 3.7GHz. You can set it to 4.1GHz instead, if your board has the right overclocking settings in the BIOS. Some of them do and some don't.
As the others said, to really overclock that CPU all the way to its maximum, you would need a P67 or Z68 board.
The integrated graphics are automatically disabled when you put a discrete graphics card in the system.