afaik, to run an ivb cpu on a z68 (or h67, h61, p67) motherboard you need to update your bios then replace the sb cpu with ivb cpu. brands like msi and asrock already made bios updates available, others may have done the same as well. check your mobo's website.
ivb's will have its own chipsets (z77, z75, h77) - those enable native usb support, more sata ports among other things.
you'll find out when ivb gets released. so far i've seen at least one 'leaked' bench with an ivb i5 on a z68 mobo. nothing is certain until intel releases ivb and officially states ivb related information.