I cant recommend a firewire HD setup, as least if you are expecting to have something that acts a real hard drive.
My firewire drive acts like a big zip drive, meaning everything has to be copied to it, instead of just being placed there as you would with a real HD. This can take 15-20 minutes or more for big files, which are what one would buy it for.
Also Firewire HDs are shaky. You keep hearing about how FW is hot-swappable. HaH. Try turning off a FWHD without first dismounting its icon (trashing it) and you are in for a lot of trouble. You've probably corrupted the drive and ruined your files, even if at first the drive doesnt act that way. So whatever you do, dont get one that looks just like the CD burner you're always turning off and on!
And if your Mac has a system freeze while the drive is mounted, it's the same as if you had turned it off without dismounting it.
In fact today i restarted my BWG3 under OSX and it warned me i had not dismounted the drive. Then the drive did not mount right away. I fear the worst, which is usually the right approach with this thing.
I would say do whatever you can to replace the drive in your computer and use an external only if all else fails.
Meanwhile, can i use the 120 WD mentioned above in my BWG3? I think im going to make a planter of the FW.