You are quite likely missing several of the SuSE supplied styles when you updated to 3.5 and many of the SuSE supplied KDE files were removed. Things like kdebase3-SuSE and others which contained many backgrounds, etc. You might still be able to install those along with the 3.5, but I'm guessing there were conflicts that were removed with your apt update. Either live with it until SuSE provides the 3.5 stuff to us or do a bit of compiling to get them back.
Interesting... I have KDE and QT as found on the 10.0 DVD. If I go to the APT repository and pull in the new QT3 and keep the existing KDE3.4.3 build from the DVD, I loose the styles. If I add in all the KDE3.5 RPMs from the APT repository, I still am missing all the styles. It seems (on my system) to be tied to the new QT3 and regardless of which kde3base-SUSE I have... when I'm using the new QT I loose the styles. What gets me is that no one else seems to have this problem when they update... yet I have it on all my installs of SUSE10.0 (when I update QT and KDE). C.