The Bootcamp 3.1 installer does not allow [some?] owners of 2006 mac pros to install 64 bit drivers. The windows installer simply wont open. Also, the support page specifically states that 2006 Mac pros are not supported.
It is possible to force the installer to go anyway (as you know), which is what this thread is about.
Like I said, HFS and "MNT" driver caused my system to go into a BSOD.
Quite a few people have had this problem
In my case, the BSOD occurred immediately after boot-up even in safe mode, meaning I was unable to remove the driver without some serious effort (I chose to just reinstall windows 7, but there are less extreme ways). This is why it is risky.