[CentOS] centos 5.5 on optiplex 745

Hi, we have some old dell optiplex 745 machines which have the Intel 965q chipset. The problem is, that they freeze as soon as the system tries to start the X system. It happens even before any log is written. This happens almost every time (for some reason it sometimes work, but 99% it fails). When i change the graphic driver in xorg.conf from intel to vesa it mostly works, but still i sometimes get a flickering screen, but this can mostly be resolved using ctrl+alt+backspace (sometimes you have to try this twice). We use the 1024x768 and 24 bit colors, so this shouldn't be the problem.

Does anyone know a fix for this problem?

Janez