Multiple Monitors (more than 2) with powerbook?

1.) That product won't work with your PowerBook.
2.) It's basically an external graphics card (not a bad one either )
3.) Not, you can't run two external monitors instead of your PB's display.

Not sure if you care, but you can run more than one external monitor (albeit not perfectly) with a VGA splitter or with a scan-converter. Decidedly old-school solutions, but I have and external monitor connected to my PB and a TV connected through a scan-converter mirroring the 2nd monitor. I use it mostly for movies/video playback.

There is also the 32MB PCMCIA video card upgrade for PB, allowing for the driving of multiple monitors. A much more elegant (and expensive) solution than above. Here is a linky:
http://www.macsense.com.au/villagetronic_vtbook.htm

FWIW...