Which generation of gfx cards started supporting 8 bit stencil buffers? I ask, since I'm making a 2d game and need this, but would like to minimize requirements.

I don't know the exact answer to your question, but take a look at this Caps Database.

For D3D I selected StencilCaps.* and the only adapters that didn't support these were Voodoo3, Rage LT Pro, Rage Pro, i815 and ViRGE DX. It may be some of those adapters support stencil using OpenGL though (I couldn't find the correct extension).

I wouldn't worry about cards not supporting stencil, just go ahead and assume the card supports it.

Thx! I checked that database. Even Riva TNT2 supports it! :D