I don't know how old is your "old" computer, but I use the 4551 inside an external USB/Firewire box to allow me to connect it to dif units, one being a P III 450 running win98 SE, and it works ok. It has Roxio burning software and no packet writing stuff.
It works ok.
In another unit P III 700 dual processor, it works ok but when I use InCD I cann't stop the firewire connect and unplugg the drive, as I can when using only Nero (Win2000).
As you see, these two units can not be considered as new.
OK I have no firewall, as I connect to the Web using Linux in the P III, whre there are no problems either, but dif firewall and OS and we can't compare.