never had this kind of error.anyway,I would avoid the a47 release,either go for A41 (last one with support for original 3dfx glides),or one of the latest releases (A58+).
the correct way would be installing manually via the device manager,there should be only one inf for opening..
that reminds me,I have actually created a custom version of the A41 driver (fixed all registry/3dfx tools related problems,readded the latest original glides and 3dfx icd to maximize compatibility with old glide/opengl games),if you want to try it out,you can find it
here (3dfx tools are not included,just get the latest standalone version from the Archive).stability or compatibily is not different from the standard release.
edit: had a nice step-by-step
how to install guide,but the pictures are all dead..well it may help a bit anyway:
http://www.falconfly.de/cgi-bin/yabb2/YaBB.pl?num=1166626980