The PXI controllers use Laptop hard drives (2.5 inch IDE)so they can be replaced in the same fashion. Replacing a HD will void any waranties you may have however, so that may or may not be a consideration for you. One consideration to think about is that we recommend using a 8.5 mm thick HD. If it is larger than 9.5 mm, it will protude a bit and block slot 2 in your chassis.
Best Regards,
Jeremy R.
NI - Applications Engineer