I got both my PC and Mac to recognize a 1 TB HD install on my MPC 5000.
Once all was good, I dragged my backup files off the PC and onto my MPC 1 TB HD (which I formatted fresh inside the MPC as opposed to using a MAC or PC to format it via USB). Everything was good for a day, then suddenly, neither my Mac PRo running OS 10.6 nor my WinXP computer could see the hard drive.
I took the hard drive out, replaced it with the original hard drive that came out of the MPC and same problem occured, so I know it isn't a 'size of the hard drive' issue. I even went so far as reformate the 1TB drive in the MPC, reinstall OS 2.0 via the CF card and install the stock HD that came in the MPC and still, neither PC or Mac systems will see the drive nor mount it via USB. I opened the case up for the fourth time, double checked all my connectors to determine that I did not inadvertatly pull anything loose when changing out the hard drive and everything looked fine. Hmmm.
heres my take on this:
There is something inherently wrong with the AKAI MPC 5000 USB firmware and Akai needs to address this ASAP. It is less than adequete, at best and seriously mercurial in its performance on both Mac and Windows platforms. I am not the only person who has had problems and complaints with the MPC series USB not performing correctly, no matter what kind of drive was used (stock or after marke)t. Furthermore, The drive is not the issue in USB mounting the MPC to your PC as I removed the drive altogether and the MPC will still boot up and run, it simply won't see an Internal Hard drive. Unlike a computer, the MPC OS is in firmware (blown onto an EPROM) hence the reason you update the firmware from a CF card and you can do so, even if an internal hard drive is NOT present . The Akai OS and its associated instructional parameters are not loading off a hard drive, say like the OS on your PC. In this, it should make no difference on how large or small a drive you use to mount and dismount via USB as the instructions used to do this are based off the firmware in the MPC itself. I know that when my USB communication was workin, after updating my hard drive, my PC saw a 945 GB hard drive. Regardless, Either the Akai sees the hard drive, or it doesn't but it has no bearing on weather the Akai will mount itself via USB to communicate with an external device. That protocol is handled in the firmware instructions when the MPC boots up and is HD irrelevant.
I know with my problem ,if the issue is not resolved, I will be returning my MPC for one that does communicate properly but this issue of USB communication, I know, from testing, is strictly internal to MPC software and has nothing to do with the Hard drive.
Guess the guy I got it from didnt have a Mac lol. Oh well, guess I gotta buy a cheap pc to go with the 5000 
Didnt have HD space to back it all up lol. Now I just gotta transfer a bunch of stuff back to MPC catch is I gotta svae to the flash card from my mac then move from flash to HD 