I had the exact same problem and temporarily fixed it by downloading an older version of libSM.6.0.0 (in libsm6_4.3.0.dfsg.1-14sarge1_i386.deb) and used it to replace the new one in /usr/lib. KDE has been working fine so far.
I hope the next upgrade to the libSM package fixes it. -- To UNSUBSCRIBE, email to [EMAIL PROTECTED] with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]