Bochs supports the emulation of 4 different 3dfx Voodoo Graphics adapter models. The Voodoo1 and Voodoo2 models are 3D-only add-on cards and require a VGA compatible primary device. The Voodoo Banshee and it's successor Voodoo3 have both a VGA core and a 2D/3D core, so no other VGA card is required. The 2D/3D cards can be assigned to AGP if the i440BX chipset is selected (slot #5).
To emulate the Voodoo1 or Voodoo2 device only the "model" parameter of the bochsrc option "voodoo" needs to be set. If the vga extension option is set to "voodoo" in that case, the primary display adapter is an ISA VGA card.
For emulating the Voodoo Banshee or Voodoo3 adapter, the vga extension option must be set to "voodoo". Using a different primary display adapter and a Banshee compatible device with it's VGA interface disabled is not implemented yet. For both Banshee and Voodoo3 there is now a specific version of the LGPL'd VGABIOS with Voodoo Banshee specific code called VGABIOS-lgpl-latest-banshee. The binary file is compiled for the Banshee PCI model, but Bochs modifies the VGABIOS data after loading to support the Voodoo3 and AGP models properly.
These bochsrc settings should be used for Voodoo Banshee PCI:
vga: extension=voodoo vgaromimage: file=VGABIOS-lgpl-latest-banshee voodoo: model=banshee
This additional setting is required for Voodoo Banshee AGP:
pci: chipset=i440bx, slot5=voodoo
To support the Voodoo3 just change the model:
voodoo: model=voodoo3