yes you can install chameleon on mac pro
yes you can use it to boot 64-bit kernel
this is one year old news.
but it does not help us anything with PC graphic cards.
it might help running mountain lion once it is out, but vital driver support for the Mac Pro 1.1 / 2.1 may be gone anyway, we don't know yet.
there's even a guide @ netkas forums.
but as I said, no real benefit can be found in this today, at least one that is worth the hassle.
if you're gonna consider hacking your way through running ML on Mac Pro 1,1, you will probably be looking at chameleon + frontported drivers, and then you might as well sell the machine for $800 and buy a hackintosh that is 2x as powerful and go through the same procedure anyway.