welcome to the forums...
any 2,5´ IDE harddrive should work - SATA drives don´t fit!
some users successfully use 160gb drives, but to be honest there is not much need for so much space.
see, even if you transfer several gb of sample libraries to the disk it is not so much fun to step through all this samples in the load screen when you decide which ones to load.
also even if you save the entire memory all the time that would be 128mb max, so a 160gb hdd would allow you to save over 1200 full loads of your memory.
anyways if you install a harddrive it is important to format it in the mpc using the format function in the utility screen since formating the drive from windows or a mac can cause problems.
peace, jo
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