I believe that your card is an AGP 1.0 spec., which is 3.3v I'm afraid.
Congratulations on not finding out the incompatability the hard way
I assume that your card is a Creative Labs or OEM product. You can get manuals from the Creative website.
As far as I know, Creative Labs owned the RIVA at that time and brought out a range of AGP and PCI cards based on the chipset.
I think they sold the video card stuff on to Nvidia a couple of years ago.
There are a few AGP 2X cards that run at 1.5v, but ALL the AGP 1.0 spec. cards ran at 3.3.
The AGP standards are a bit confusing, to say the least! AGP 1.0 had a multiplier of 1X or 2X, a voltage of 3.3 and a type 1 slot. AGP 2.0 had a multiplier of 2X or 4X, 1.5v and type 2 slot. AGP 3.0 (current) is 8X, 0.8v and type 2.
So there are some APG 2X cards that could be either 3.3 or 1.5v.
Yours is 2X, but I'm pretty sure it's 3.3v.
HTH
SD