Thank you for info; didn't help but I found out that the Xwindows library for display (SIS630/730) provided by Mandriva is not correct and dated May 2006. The name of this library is sis_drv.so and can be found in /usr/lib/xorg/modules/drivers. It should be replaced by a new version compatible with Xwindows 7.1.1 and can be found on the site www.winischhofer.at
(redirection). This version of sis_drv.so binary file is dated as August 2006. I did it and it solved the problem; KDE could appear finally. The SIS company was bought by another company and does not support drivers for XWin.
Hope it can help others, since it took me quite a while to figure out , as a novice Linux adept. Merry Xmas and Xwindows !