Go for 250mb zips!!!!
I already use the set-up you are looking into.
I've got an MPC2000 with a 250mb scsi zip & a Mac G4 with a 250mb USB zip. Format all your zip disks on the MPC.....the Mac will happily read those but I don't think the MPC likes a Mac formatted disk.
If you want to edit your MPC samples on the Mac you need to save them in .wav format on the MPC unless you get hold of MpcPgmMaker, which is a Mac program that converts MPC .snd samples to .wav or .aiff & can also set up MPC .pgms
http://homepage.mac.com/seishu/ssworks/MpcPgmMaker.html