There's a new SiS AGP driver out. This time its version 1.17e WHQL for the following chipsets:

SiS540, SiS630, SiS630ET, SiS630E, SiS630S, SiS630ST, SiS635, SiS645, SiS645DX, SiS648, SiS650, SiS651, SiS730S, SiS730SE, SiS735, SiS740, SiS745, SiS661FX, SiS760.