MB TYAN TOMCAT I845GL (S2098AGN)

Hi all, who form you have some experience with KDE on the integrated graphics adapter on the TYAN TOMCAT i845GL motherboard? My problem is simple: with my actually M/B (ASRock with integrated graphics adapter -SiS 660-) it isn't possible to switch between users as I can with -for example- the nVidia graphics card that I have on my other system (I use SuSE 9.3 with KDE 3.4.0 level b on both systems), Thank you, any suggestion are great welcome! Stefano