I found the tech agreement between Sega and 3DFX.  The release of this document at 3DFX's IPO was one of the first fatal mistakes the company made. 

Sega / 3DFX Technology & License Agreement http://www.techagreements.com/agreement-preview.aspx?num=41001&title=Sega/3DFX-T...

More public releases are listed at the bottom of the page.

Probably when they were developing the Dreamcast Prototypes...

The final Prototype they chose was from PowerVR - The Katana...this became the Dreamcast.

But the 3Dfx prototype (called Black Belt) - only one example exists of this prototype...the likelihood ANY of us will see it up close is NIL!

And now MANY links :

http://assemblergames.com/forums/showthread.php?t=90
http://www.tomshardware.com/forum/130116-33-what-3dfx-chip-sega-black-belt-proto...
http://www.nvnews.net/vbulletin/showthread.php?t=29935
http://forums.sega.com/showthread.php?p=488012
http://forums.firingsquad.com/t5/Consoles-General-Discussion/picture-of-Sega-s-3...
http://www.consolepassion.co.uk/sega-dreamcast.htm
http://www.neogaf.com/forum/showthread.php?t=345469
http://sega.wikia.com/wiki/Dreamcast
http://www.segatech.com/technical/gpu/index.html