Well they will both perform about the same in everyday task the I7 720 will only really shine when it comes to heavily multi-threaded apps but it is horrible on your battery. So if you just need it for basic everyday task like word processing and surfing on the internet for research or what not. The I5 should be your choice, the I5 will also have no problems with games depending on your video cards in the laptops. The I7 IMO is overkill for most people on a laptop.
the i5 has integrated graphics, but if i have an ATI card in the laptop will i be able to switch between integrated graphics and the ATI card (like the m11x can)?
That is something you would have to find out from the manufacturer most laptops you wont be able to add a dedicated card.