It doesn't look like a Cardbus adapter, but as long as it's the right form factor (PC card) and it does what you want, that should be fine. Not being Cardbus, it might be a bit slower, but it might just work as a generic storage device on your PB. It doesn't say it works with OS X, but it might...
I had thought you were looking for something to go beyond USB 1.1 speeds (and I may be wrong about the speed of your PB's USB ports), thus the confusion.