Ok.
First of all, I suggest ALWAYS using Western Digital Caviar drives. Reliable, and affordable. Don't use a FireWire hdd unless you have no internal bays/ide connections left, it requires an extra power outlet, costs more, due to the case, and takes up extra room. USB is pathetic for even a floppy drive so dont even bother.
Now. as for the 137 Gb limit, it's nothing to do with mac.
ATA as we know it, (ATA-33, 66, 100, 133) is limited to 137Gb per drive. Serial ATA (under development) has a theoretical limit of some stupid amount like 60 000 terabytes. however, the largest ata drive i know of is a Western Digital 130 Gb drive. i somehow doubt you need that much space. if you do, buy a FireWire cd-rw and burn some of you stuff to cd.