What mother board are you using? Sometimes to get a board to regognize a newer model the BIOS need to be flashed to the latest version. For examplpe I have a Celeron2 533 that one of my old boards was recognizing as a P3 533 instead of a C2 533. After a BIOS flash it was recognized as a Celeron 2.
What brand card is it?
You can use a program like Sisoft Sandra or 3DMark2001 to identify the card as well.
When it boots and you get the VGA BIOS come up (first one - the one b4 the memory count) it should say what type of chip board it is. Make a note of the Video BIOS revision number as it will also tell you what chip it uses.
Nvidia's internal code for the chips is NVaa (where aa = numbers mentioned above).
I have to say that my Geforce 1 SDR is recognised as a Geforce 256 by the Detonator .inf file (Windows matches the hardware's Hardware ID to the one in the drivers inf file. This is how it knows which drivers to install and selects the name accordingly).
If you've got SiSoft Sandra (if not download it). Open PCI,AGP and Cardbus information subsection (icon like a PCI card). Select AGP bus from the top drop-down box and there should be only one option in the lower dropdown box. It will list the OEM device name if it mentions NV15 it will an Geforce 2 or if it says NV10 then it is a Geforce 1.
Also look at the Video system information in Sandra as well.
Looking at your 3Dmark benchmarks in your other post suggests that with the "Geforce 2 GTS" isn't setup correctly.
If it is a Geforce 1 SDR then it has the same memory bandwidth as a Geforce 2MX(128bit memory bus @ 166). If you have run the default benchmark of 1024x768x16bit then the bottle neck should be the same onn a Geforce SDR or Geforce 2MX (irrespective as whether the CPU or video card is limiting).
Neither the Voodoo3 or the Geforce 2's (GTS or MX) support SBA (side-band addressing) but some Geforce 1 do. Try disabling the SBA in your BIOS and make sure AGP 2x is enabled in the BIOS.
Try reinstalling DirectX 8.0a.
The Voodoo3 doesn't use most of the AGP functions so they aren't fussy about the setup (They simply treat the AGP port as a PCI66 bus).