I'd second the suggestion that you might want to consider using an x86 Intel box (the cheapest rotgut machine you can find that takes SATA drives would do if you don't want to use your existing Linux machine) as a Linux/NetaTalk/Samba server instead of the B&W. A B&W will adequately perform basic server functions if you slap an old version of OS X Server on it but of course if you want to be legal an OS X Server license is expensive, a B&W has those disk size limitations, and the versions of OS X Server which support acting as a Time Machine target for your MBP (Leopard or better) won't run on a B&W. (Netatalk was recently updated to support Time Machine.)

If you were to install Linux on the B&W you *may* be able to break the PATA drive size limitation, but don't quote me on that. (I've found on x86 machines Linux can work around most BIOS limitations including the 128GB limit by probing the hard disk directly and asking for its geometry. Linux of course substitutes its own LBA48 compliant driver for the BIOS one so the hardware isn't a problem. The only limitation you're then stuck with is you have to have a boot partition that resides entirely within the BIOS-supported hard disk space.) I've never run a gigantic IDE hard disk with PPC Linux and some of the Google hits I've seen imply that on Macs Linux depends on Open Firmware to get the drive size correct.