Hi guys,I'll be getting an powermac g4 (for free) and I was thinking of putting there my voodoo 3 3000,can I flash it to "mac version" or it isn't necessary?
Other thing,the drivers available support wich versions of macos?

Hi,
You will need to flash the card to Mac.

Install the V3 into a pci slot behind the original card.
The V3 will be seen as a "display card".
Run the "FlashROMVoodoo3.sea"
Follow the instructions.
Enter when asked the name of the mac bios :
V3-166-5-29-2000.rom
or
V3-143-5-29-2000.rom
depending your card (V3 3000 or V3 2000)

Once you answered "y" to the question "are you sure you want to use this image file", the utility will save the pc rom on your disk (if you want to use later your V3 in a PC) then will install the mac bios.
You will need then to shutdown and restart the machine to get the V3 recognized by the system.
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According the readme file inside the driver :
Installing the Voodoo3¨ in your Macintosh

Before installing the drivers, the Voodoo3 board should be installed into any available PCI slot in your Macintosh system.  Please consult the documentation that came with your system for instructions on how to install PCI expansion cards in your system.   It is not necessary for a monitor to be connected to the Voodoo3¨ card for the driver installation phase.

Installing the Voodoo3¨ drivers

To install the Voodoo3¨ drivers, drag the four files in the "into Extensions Folder" into your Extensions folder.  This may be done easily by dragging the files over your System Folder icon.  MacOS will notify you that the files need to be placed into the Extensions folder automatically.  Click on OK and MacOS will copy the files for you.

Updating the ROM image

Before the Voodoo3 will be usable, you must run the FlashROMVoodoo3 Application found in the ROM folder of the drivers archive.   When you run this application, a console will open that will display a list of all Voodoo3¨ based boards found in your system, along with which slot they are installed in.   Choose the number of the board you wish to update, or choose 0 to abort the update utility.

After choosing the board, the update utility will examine the ROM on the board and tell you that the ROM either contains a PC BIOS image, or contains an OpenFirmware image.   If will then ask you if you are sure you want to update the BIOS on that board.

If you enter 'y', then you will be prompted for the filename of the ROM image to use.  This will be something like "V3P143-MM-DD-YYYY.rom" for the Voodoo3¨ 2000, or "V3P166-MM-DD-YYYY.rom" for the Voodoo3¨ 3000.

Once you enter the ROM, the update utility will examine it and determine whether it is a PC BIOS image or an OpenFirmware image and prompt you again to make sure that this is the ROM image you wish to use.

After choosing 'y', the utility will save the existing ROM image to disk as either PC-SAVE.ROM or MAC-SAVE.ROM depending on the current ROM image on the board, and will begin the process of updating the flash ROM on the Voodoo3 board.

IMPORTANT: If this is the first time you are flashing the ROM, please save a copy of the PC-SAVE.ROM file in a safe place in case you ever need to use the Voodoo3¨ in a PC. If you don't save a copy, it will be overwritten the next time you update the ROM.   As a safety measure, the new FlashROMVoodoo3 utility will not allow you to specify names of "PC-SAVE.ROM" or "MAC-SAVE.ROM" for the source BIOS name.

After the ROM has been updated, you must restart your computer for the Voodoo3 to be recognized by thesystem.   If you do not yet have a monitor connected, then you may shut down, connect a monitor and then turn your system back on.

Removing the Voodoo3¨ drivers

If you wish to remove the Voodoo3¨ drivers, simply drag the following files from your Extensions folder into the trash:

3dfx GlideLib2.x
3dfx GlideLib3.x
3dfx Graphics Accelerator
3dfx Hardware Resource Manager
3dfx OpenGL Renderer

You will not be able to delete all of them permanently (by emptying the trash) until you reboot your system.

Thanks a lot Nightbird,but I have an AGP V3 3000,so no way it will work right?

That would be possible according to this review though they didn't try.
I quote "The AGP version of the card can be flashed with the Voodoo3 ROMs and used in a Power Mac G4, replacing the built-in AGP graphics card. Macworld Lab did not test this configuration"