NO! There are a few reasons. First of all, yes hardware decoding should work somewhat well. The thing you need to know is that the bandwitdh of USB is no where NEAR enough to let you use that PCMCIA decoder reasonably. Here is what this leaves you with:
1) A mini-pci DVD decoder
2) Some sort of mini-pci to full PCI slot adapter (seriously doubt this is avalible, you could make it yourself but...)
3) Doing the decoding on another PC, and sending it over ethernet (you'd need a mini-pci ethernet card for this, USB still doesn't have that kind of bandwidth) and then displaying it.
4) You could rip the DVDs to uncompressed AVI files and store them somewhere, then watch those on the Webplayer getting them from a network drive.
5) This one is my personal favorite for the pure geekyness of it: get a PCI socket and wire it up by hand soldering wires to it and the chipset, to give you a working PCI slot. Would be hard as hell and you'd need some other chips but if this is possible it would be cool as hell.
That company you found is interesting, but the fact is this: that is really designed for PCMCIA compact flash adaptors, modems, gameports, and other simple things.
MOST IMPORTANT PART:
That DVD PCMCIA card requires what's called ZoomVideo (and I'm not suprised). This is basically direct access to the framebuffer/video hardware, and is in most laptops going back a few years. It is IMPOSSIBLE over USB. I thought so. Sorry. You still have the first few options I gave you.