10.6.3 update problem

I am at my wits end by now. I have installed OS X 10.6 on my Dell Studio XPS 16 laptop several times now fine, using the retail disc with the Empire EFI 1.085 boot cd. However, I desperately need to update to at least 10.6.2 to get support for my graphics card.

Unfortunately, every time i install an update I get problems, I've made about 5 or 6 attempts now, and after each attempt my OS X partition no longer boots. My last attempt was to install just the 10.6.2 combo update to see if that made a difference, and this is the sequence of events:

-I installed 10.6 with the Empire EFI boot disc, it boots in safe mode
-Using MultiBeast, I installed FakeSMC, NullCPUPowerManagement, LegacyAppleRTC, and EvOreboot kexts, and rebooted (again in safemode)
-I installed the 10.6.2 combo update and rebooted as the installer requires
-the Boot hangs, the last three lines are:

DSMOS has arrived
FakeSMC: key info not found MSDS, length - 6
ACPI_SMC_PlatformPlugin : :start - waitForService(resourceMatching(AppleIntelCPUPowerManagement) timed out

In my previous attempts, I sometimes had a kernel panic that referenced something about the IONetworkFamily Kext already being loaded, one install would hang at the same lines as above but also give me two lines that said Error something, and I also had two installs that gave me a kernel panic that referenced three IOsomething kexts.

Note: I believe that this boot cd automatically makes a boot verbose, as regardless of my boot commands I don't get a graphic boot, but using another boot cd, prior to the update it ends in a garbled/blocky screen as my graphics isn't supported, and after the update I get the spinning loading thing under the apple logo and then a message pops up in a dark grey box saying I need to restart my computer

These are the basic specs of my system:
Dell Studio XPS 16 laptop (intel pm55 chipset)
Intel Core i7 720QM processor
ATI Radeon Mobility HD 4670

Can anyone please help?